Resolution dropdown, list-focus preservation, unified dark theme, startup logging, and memory map

- Bottom-bar resolution dropdown (1080p60/1080p30/720p60/480p30) with tooltip
  on finding upload bandwidth; disabled while live; no in-app speed test
- FocusPreservingListBox keeps selection/focus coherent when a selected
  scene/source is deleted (skip hidden scenes; leave list when empty)
- Themes/Controls.xaml: single dark-theme dictionary merged once in App.xaml;
  custom ComboBox template fixes SelectionBoxItem rendering; GoLiveWindow and
  ReuseImageDialog consolidated onto shared styles
- AppLog file logger + AppDomain/Dispatcher exception hooks; checkpointed
  MainWindow/VM/dialog constructors (caught MenuItemRole.Separator XAML crash)
- Memory map: schema.md conventions, per-directory index.md, updated ai.md/
  TASKS.md/README.md (OAuth creds real; token persistence still pending)

Models/QualityOption.cs

@@ -0,0 +1,10 @@
+namespace ytLive.Models;
+
+/// <summary>
+/// A resolution tier offered by the bottom-bar dropdown. Bitrate is Mbps.
+/// </summary>
+public sealed record QualityOption(string Display, int Fps, double Bitrate)
+{
+    /// <summary>Self-documenting label, e.g. "1080p60 (8Mbps)".</summary>
+    public string Label => $"{Display} ({Bitrate:0.#}Mbps)";
+}

Models/index.md

@@ -0,0 +1,15 @@
+# Models — index
+
+Plain data types. No logic beyond what a property can carry. See
+[`schema.md`](../schema.md) for the memory-map conventions.
+
+| File | Purpose |
+|------|---------|
+| `Scene.cs` | A scene: `Name`, `IsHidden`, `IsChatScene`, `IsEditing`, `Sources` collection |
+| `Source.cs` | A source: `SourceType` enum (Image/Webcam/Screen/Background/Text), `X`/`Y`/`Width`/`Height`, `Opacity`, `IsEnabled`, `ImageSource`, asset identity |
+| `QualityOption.cs` | Resolution tier record `(Display, Fps, Bitrate)`; `Label` formats as `1080p60 (8Mbps)` — drives the bottom-bar dropdown |
+| `StreamConfig.cs` | `StreamConfig` (note: `TargetBitrate`/`Resolution` defaults are stale — not yet wired to the dropdown), `StreamHealth` (bitrate/FPS/dropped/duration), `StreamStatus` enum |
+| `YouTube.cs` | `YouTubeChannel` and `ChatMessage` (chat feed) |
+
+Related: [`ViewModels/index.md`](../ViewModels/index.md) consume these;
+[`Services/LayoutStore.cs`](../Services/LayoutStore.cs) persists `Scene`/`Source`.