feat(preview): right-click is the menu, zoom is the single-handed gesture

Creator ruling 2026-11-01, and the reason is live-stream ergonomics: no two-handed
chords while a broadcast or recording is running.

- Edit mode: left selects / drags / resizes, right opens the context menu, Ctrl+right
  toggles the zoom box. Chords are acceptable here because editing is a stopped activity.
- Preview mode: left toggles the zoom box, right opens the context menu, and Ctrl+right
  is swallowed outright — handled rather than left to fall through, so Ctrl+right cannot
  open a menu by accident while one hand is on the mouse.

This also removes the old live behaviour where right-click activated the magnifier at the
cursor point (and dismissed it). Zoom in preview is now a plain toggle; if point-zoom is
wanted back it needs a one-button gesture, not a chord.

Build: Release 0 warnings. Debug is currently blocked by the running app holding the exe
(PID 47252) — close it and the Debug build copies normally.

docs/ai/ui-surface.md

@@ -104,6 +104,7 @@ The app is a **director's control surface**, not an editor. This replaces the OB
 
 - **Left panel:** `EditingActive` is an explicit `EDIT` toggle, not a mode inferred from `StreamStatus`. On = scene layers + properties; off = YouTube chat. Go Live turns editing off and stopping restores it; recording does not automatically switch it off. The staged scene is the preview/edit target; `LiveScene` is the program output.
 - **Top bar:** the `EDIT` toggle sits beside the REC/ON-AIR session controls; the brand and account surfaces remain at the sides. Its **right edge aligns with the layers panel below** (`TopBar` column 0 is a fixed **352** = work-area margin 8 + 360px column − the bar's own 16px padding), so the button and the panel share an edge. The **settings gear moved to the preview rail** (2026-11-01): first tab, orange (`Brush.Attention`), gear icon only — left-click opens the app menu (Settings / Bug / Feature / About), right-click goes straight to App Settings.
+- **Preview gestures (2026-11-01):** *edit mode* — left selects/drags/resizes, right opens the context menu, **Ctrl+right toggles the zoom box**. *Preview mode* — **left toggles the zoom box**, right opens the context menu; **Ctrl+right is swallowed** (no chord while live or recording — one hand, always). Menus exist on the webcam layer and the backdrop; every other layer right-clicks through to the backdrop menu. Left-dragging with the zoom box open moves it, in both modes.
 - **Preview undo/redo (2026-11-01):** `Ctrl+Z` / `Ctrl+Shift+Z`, window-level bindings, live only while `EditingActive` — undo with the preview showing program output would rewrite a scene nobody is looking at. `Models/PreviewHistory` snapshots element **references** plus geometry, visibility, order and membership, so move / resize / reorder / add / remove / hide all undo in one step per gesture (`PushPreviewUndo` is called once at drag or resize start, never inside the move loop). Property edits (colour, opacity, border, font) are **not** captured yet — stated in the type's doc comment so nobody assumes otherwise. The stack clears on layout load. Guard: `ytLive.Tests/PreviewHistoryTests.cs`.
 - **Developer affordances are compiled out of release, not hidden.** Any control that must never ship (today: the all-resolutions override) lives in its own `UserControl` whose `Page` and `Compile` items are removed by `ytLive.csproj` when `$(Configuration) != 'Debug'`, and is added to its host at runtime inside `#if DEBUG` (`OverlayHost`). A collapsed row still exists in the visual tree of every shipped copy; "not compiled" is the only claim worth making. Label such rows with `Brush.Attention` (orange) while they are visible in Debug. Guard: `ytLive.Tests/OutputProfileTests.cs` asserts the build rule, and `Helpers/DevBuild.cs` is the single source for "is this a dev build".
 - **Scene strip:** five fixed-size cards above the preview show the scene name and hotkey; the staged scene carries a `PROGRAM` badge, and staged/live borders use orange. Click stages a scene while idle; while streaming or recording it changes program output and starts the selected transition.