feat(socials): bar appearance — text colour, background plate, opacity, text shadow

In the Socials drawer, under the show/hide switch: text colour, an optional background plate
with its own colour and opacity, and a text drop shadow. The bar had been hard-wired
white-on-transparent since it shipped.

- `SocialsConfig` gains five additive properties (BarTextColor, BarBackgroundEnabled,
  BarBackgroundColor, BarBackgroundOpacity, BarTextShadow).
- Persistence: five new Socials columns, added by the per-column idempotent migration pattern
  (a half-migrated DB heals instead of failing), written in Save and read back in Load with
  defaults for pre-existing rows.
- `SocialBarRenderer.Render(entries, SocialBarStyle?)` — the look is a separate value type so the
  renderer stays a pure "entries + look" function and the preview can never read a half-applied
  config mid-edit. A malformed hex falls back to white/black instead of throwing inside a render
  tick.
- The plate hugs the entries (rounded 20px, padding) so it reads as a caption bar, not a band
  across the frame. Off by default, because transparent is what creators have today.
- The colour pickers reuse `BorderColorPalette` — one catalogue of the app's colours, per the
  TASK 60/63 rule.

Guard: SocialBarAppearanceTests paints the real strip and inspects pixels — default is white with
no plate, a red text colour reaches the glyphs, a 55% blue plate yields half-transparent blue
pixels, and the shadow adds dark pixels that were not there before.

Services/Compositor/SocialBarRenderer.cs

@@ -33,8 +33,11 @@ public static class SocialBarRenderer
     public const int Width = 1920;
 
     /// <summary>Returns the strip frame, or null when there is nothing to render.</summary>
-    public static VideoFrame? Render(IEnumerable<SocialEntry>? entries)
+    public static VideoFrame? Render(IEnumerable<SocialEntry>? entries, SocialBarStyle? style = null)
     {
+        var look = style ?? SocialBarStyle.Default;
+        var textBrush = look.TextBrush;
+        var glyphEffect = look.TextShadow ? ShadowEffect() : null;
         var list = entries?.Where(e => e != null).ToList();
         if (list == null || list.Count == 0) return null;
 
@@ -51,7 +54,8 @@ public static class SocialBarRenderer
             item.Children.Add(new Path
             {
                 Data = Geometry.Parse(entry.LogoData),
-                Fill = Brushes.White,
+                Fill = textBrush,
+                Effect = glyphEffect,
                 Width = 24,
                 Height = 24,
                 Stretch = Stretch.Uniform,
@@ -60,7 +64,8 @@ public static class SocialBarRenderer
             item.Children.Add(new TextBlock
             {
                 Text = entry.Handle,
-                Foreground = Brushes.White,
+                Foreground = textBrush,
+                Effect = glyphEffect,
                 FontSize = 14,
                 VerticalAlignment = VerticalAlignment.Center,
                 Margin = new Thickness(8, 0, 0, 0),
@@ -77,7 +82,22 @@ public static class SocialBarRenderer
             Effect = new DropShadowEffect { Color = Color.FromRgb(0x2e, 0xcc, 0x71), BlurRadius = 18, ShadowDepth = 0, Opacity = 0.9 },
         };
         var centered = new Grid { HorizontalAlignment = HorizontalAlignment.Center, Margin = new Thickness(0, GlowPad, 0, 0) };
-        centered.Children.Add(row);
+        if (look.BackgroundEnabled)
+        {
+            // The plate hugs the entries, so it reads as a caption bar rather than a band across
+            // the frame; 20px radius matches the pill language used elsewhere.
+            centered.Children.Add(new Border
+            {
+                Background = look.BackgroundBrush,
+                CornerRadius = new CornerRadius(20),
+                Padding = new Thickness(18, 6, 18, 6),
+                Child = row,
+            });
+        }
+        else
+        {
+            centered.Children.Add(row);
+        }
         container.Children.Add(centered);
 
         container.Measure(new Size(Width, height));
@@ -102,4 +122,52 @@ public static class SocialBarRenderer
 
         return new VideoFrame(Width, height, pixels);
     }
+
+    private static DropShadowEffect ShadowEffect() => new()
+    {
+        Color = Colors.Black,
+        BlurRadius = 4,
+        ShadowDepth = 2,
+        Direction = 315,
+        Opacity = 0.85,
+    };
+}
+
+/// <summary>How the social bar is painted (creator request 2026-10-30: text colour, an optional
+/// plate with its own colour and opacity, and a text drop shadow).
+///
+/// <para>It is a separate value type, not <see cref="SocialsConfig"/>, so the renderer stays a
+/// pure function of "entries + look" and the preview/output can never read a half-applied
+/// config mid-edit.</para></summary>
+public readonly record struct SocialBarStyle(
+    string TextColor,
+    bool BackgroundEnabled,
+    string BackgroundColor,
+    double BackgroundOpacity,
+    bool TextShadow)
+{
+    public static SocialBarStyle Default => new("#FFFFFF", false, "#000000", 0.55, false);
+
+    public static SocialBarStyle From(SocialsConfig? config) => config is null
+        ? Default
+        : new(config.BarTextColor, config.BarBackgroundEnabled, config.BarBackgroundColor,
+              config.BarBackgroundOpacity, config.BarTextShadow);
+
+    /// <summary>Glyph colour. A malformed hex falls back to white rather than throwing inside a
+    /// render tick — a bad colour must never kill the output.</summary>
+    public SolidColorBrush TextBrush => Solid(TextColor, 1.0, Colors.White);
+
+    /// <summary>Plate colour carrying the configured opacity in its alpha.</summary>
+    public SolidColorBrush BackgroundBrush
+        => Solid(BackgroundColor, Math.Clamp(BackgroundOpacity, 0, 1), Colors.Black);
+
+    private static SolidColorBrush Solid(string hex, double opacity, Color fallback)
+    {
+        Color colour;
+        try { colour = (Color)ColorConverter.ConvertFromString(hex); }
+        catch (Exception) { colour = fallback; }
+        var brush = new SolidColorBrush(Color.FromArgb((byte)Math.Round(opacity * 255), colour.R, colour.G, colour.B));
+        brush.Freeze();
+        return brush;
+    }
 }

Services/LayoutStore.Load.cs

@@ -50,7 +50,11 @@ public partial class LayoutStore : IDisposable
 
         using (var cmd = _connection.CreateCommand())
         {
-            cmd.CommandText = "SELECT Id, BarPosition, BarEnabled FROM Socials LIMIT 1;";
+            cmd.CommandText = """
+                SELECT Id, BarPosition, BarEnabled, TextColor, BackgroundEnabled,
+                       BackgroundColor, BackgroundOpacity, TextShadow
+                FROM Socials LIMIT 1;
+                """;
             using var reader = cmd.ExecuteReader();
             if (reader.Read())
             {
@@ -58,6 +62,11 @@ public partial class LayoutStore : IDisposable
                 {
                     BarPosition = Enum.TryParse<SocialBarPosition>(reader.GetString(1), out var pos) ? pos : SocialBarPosition.Bottom,
                     BarEnabled = reader.FieldCount > 2 && !reader.IsDBNull(2) && reader.GetInt32(2) != 0,
+                    BarTextColor = reader.FieldCount > 3 && !reader.IsDBNull(3) ? reader.GetString(3) : "#FFFFFF",
+                    BarBackgroundEnabled = reader.FieldCount > 4 && !reader.IsDBNull(4) && reader.GetInt32(4) != 0,
+                    BarBackgroundColor = reader.FieldCount > 5 && !reader.IsDBNull(5) ? reader.GetString(5) : "#000000",
+                    BarBackgroundOpacity = reader.FieldCount > 6 && !reader.IsDBNull(6) ? reader.GetDouble(6) : 0.55,
+                    BarTextShadow = reader.FieldCount > 7 && !reader.IsDBNull(7) && reader.GetInt32(7) != 0,
                 };
                 var socialsId = reader.GetString(0);
 

Services/LayoutStore.Migrations.cs

@@ -591,11 +591,23 @@ public partial class LayoutStore : IDisposable
                 columns.Add(reader.GetString(1));
         }
 
-        if (columns.Contains("BarEnabled")) return;
+        // Each column is added on its own, guarded by presence — the same idempotent pattern the
+        // webcam table uses, so a half-migrated DB heals instead of failing.
+        AddColumnIfMissing("BarEnabled", "INTEGER NOT NULL DEFAULT 1");
+        AddColumnIfMissing("TextColor", "TEXT NOT NULL DEFAULT '#FFFFFF'");
+        AddColumnIfMissing("BackgroundEnabled", "INTEGER NOT NULL DEFAULT 0");
+        AddColumnIfMissing("BackgroundColor", "TEXT NOT NULL DEFAULT '#000000'");
+        AddColumnIfMissing("BackgroundOpacity", "REAL NOT NULL DEFAULT 0.55");
+        AddColumnIfMissing("TextShadow", "INTEGER NOT NULL DEFAULT 0");
 
-        using var alter = _connection.CreateCommand();
-        alter.CommandText = "ALTER TABLE Socials ADD COLUMN BarEnabled INTEGER NOT NULL DEFAULT 1;";
-        alter.ExecuteNonQuery();
+        void AddColumnIfMissing(string name, string spec)
+        {
+            if (columns.Contains(name)) return;
+            using var alter = _connection.CreateCommand();
+            alter.CommandText = $"ALTER TABLE Socials ADD COLUMN {name} {spec};";
+            alter.ExecuteNonQuery();
+            columns.Add(name);
+        }
     }
 
     // v8 → v9: SocialEntry gains Software (the fediverse instance's nodeinfo

Services/LayoutStore.Save.cs

@@ -314,11 +314,20 @@ public partial class LayoutStore : IDisposable
             var socialsId = Guid.NewGuid().ToString();
             using (var cmd = _connection.CreateCommand())
             {
-                cmd.CommandText = "INSERT INTO Socials (Id, BarPosition, BarEnabled) VALUES ($id, $pos, $enabled);";
+                cmd.CommandText = """
+                    INSERT INTO Socials (Id, BarPosition, BarEnabled, TextColor, BackgroundEnabled,
+                                         BackgroundColor, BackgroundOpacity, TextShadow)
+                    VALUES ($id, $pos, $enabled, $text, $bgen, $bg, $bgopacity, $shadow);
+                    """;
                 cmd.Transaction = tx;
                 cmd.Parameters.AddWithValue("$id", socialsId);
                 cmd.Parameters.AddWithValue("$pos", socials.BarPosition.ToString());
                 cmd.Parameters.AddWithValue("$enabled", socials.BarEnabled ? 1 : 0);
+                cmd.Parameters.AddWithValue("$text", socials.BarTextColor);
+                cmd.Parameters.AddWithValue("$bgen", socials.BarBackgroundEnabled ? 1 : 0);
+                cmd.Parameters.AddWithValue("$bg", socials.BarBackgroundColor);
+                cmd.Parameters.AddWithValue("$bgopacity", socials.BarBackgroundOpacity);
+                cmd.Parameters.AddWithValue("$shadow", socials.BarTextShadow ? 1 : 0);
                 cmd.ExecuteNonQuery();
             }