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)

Themes/index.md

@@ -0,0 +1,24 @@
+# Themes — index
+
+The single source of the dark UI theme. See [`schema.md`](../schema.md) for the
+memory-map conventions.
+
+| File | Purpose |
+|------|---------|
+| `Controls.xaml` | All custom control styles/templates: `YtButton`, `YtButtonSecondary`, `IconButton`, `YtTextBox`, `YtComboBox`, scrollbar/slider/tooltip/context-menu/menu-item/separator/list-item (implicit where app-wide), `YtListBoxItem`, `YtLabel`, `SectionHeader` |
+
+How it's wired:
+- Merged once in [`App.xaml`](../App.xaml) — app-wide. New windows get the theme
+  automatically; **do not re-merge per-window**.
+- Palette: window `#1a1a2e`, fields `#0f3460`, borders `#2a3a5e`, popups
+  `#16213e`, accent `#e94560`, hover `#26ffffff`, text `#e0e0e0`.
+
+Gotchas learned the hard way:
+- `MenuItemRole` has **no `Separator` value** — separators are standalone
+  `Separator` controls with their own implicit style.
+- A custom `ComboBox` template must put the `ContentPresenter` (`SelectionBoxItem`)
+  **inside the ComboBox template, not the ToggleButton template** — the latter
+  resolves against the wrong TemplatedParent and renders nothing.
+
+Related: [`Helpers/index.md`](../Helpers/index.md) (custom controls the theme
+styles), the XAML files at repo root that consume these styles.