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)";
+}