Control Surface UX: pill toggle, background rename, per-scene properties

- Sliding pill toggle (green ON / red OFF) replaces checkbox
- Geometry mismatch error for custom backgrounds
- Backdrop -> Background: C# rename, SQL column rename with migration
- Source.IsBackground: new -> override (fixes WPF binding)
- Legacy 'Backdrop' display name migrated to 'Background'
- Per-scene UseDefaultBackground + CustomBackgroundPath
- Asset files renamed backdrop -> background
- StagedScene/LiveScene split, thumbnail strip, edit gating
- TransitionService (Cut/Fade/Move)
- Context menu: Capture Desktop, Refresh Desktop
- Resolution badge removed, ON-AIR status light added

ai.md

@@ -14,6 +14,24 @@ Skip feature pitch, step-by-step implementation plans, pros/cons tables, and
 "potential pitfalls" sections unless the user explicitly asks for a plan first.
 A short diff-style summary beats a proposal document every time.
 
+## LAN infrastructure (192.168.50.x)
+
+All LAN credentials live in `CREDENTIALS.md` (gitignored). Server IPs and roles:
+
+| Host | IP | Role |
+|------|----|------|
+| corsair | .132 | Gaming/streaming primary — RTX 5070 Ti (this machine) |
+| llamavault | .86 | ODROID-HC4, 12TB RAID5, media storage (NFS). SSH: `ssh mshallop@192.168.50.86` |
+| pivault | .158 | RPi5 8GB, 10.83TB RAID5 NAS |
+| jarvis | .210 | AMD Ryzen 5 5600X, RX 6600 XT — AI inference, SearXNG, Docker registry, Immich |
+| ultron | .108 | AMD Ryzen 7 7840HS — AI orchestrator, llama-server, Qdrant |
+| gordito | .144 | Home Assistant, Alarmo, Zigbee |
+| officerfriendly | .26 | Pi-hole DNS |
+| octopi | .197 | OctoPrint (Prusa MK4) |
+| BigBlinkyRouter | .1 | ASUS ROG GT-BE98 Pro, WiFi 7 |
+
+Web infra (DO droplet): `llamacasty.com` + `llamachile.tube` at `143.244.176.131`.
+
 ### No-Fluff Mode (on demand)
 
 Invoke with "no-fluff mode" (or similar) when you want ruthless review instead
@@ -70,13 +88,13 @@ Good Dog Rule: ONE integration test per branch, ONE test per PR. Current: TokenS
 roundtrip/corrupt/missing/clear, OAuth exchange/refresh/ClearSession, CameraManager refcount +
 frame pump + failure handling (fakes for the WinRT seams), real-`MainWindow` round-clip
 interaction test, LayoutStore delete roundtrip, LayoutStore pre-round-rect-dims roundtrip,
-LayoutStore backdrop roundtrip, LayoutStore HasBackdrop roundtrip + v5→v6 non-Live backfill,
+LayoutStore background roundtrip, LayoutStore HasBackground roundtrip + v5→v6 non-Live backfill,
 ScreenCaptureManager refcount + shared-bitmap + coalescing
-(fake `IScreenCaptureSource` + a real background-STA `Dispatcher`), BackdropTests (EnsureBackdrop
-insert/idempotent/heal + HasBackdrop gate, IsLiveCapture, DisplaySource, INPC), SceneCatalogTests
-(the five canonical scenes, Live-only backdrop policy, EnforceBackdropPolicy), WebcamSafeguardTests
+(fake `IScreenCaptureSource` + a real background-STA `Dispatcher`), BackgroundTests (EnsureBackground
+insert/idempotent/heal + HasBackground gate, IsLiveCapture, DisplaySource, INPC), SceneCatalogTests
+(the five canonical scenes, Live-only background policy, EnforceBackgroundPolicy), WebcamSafeguardTests
 (the per-scene size clamp incl. the Chat half-screen-area cap), SceneCompositorTests (the full-scene
-composite integration test: backdrop + round webcam + mirrored/bordered images + flash; the vertical
+composite integration test: background + round webcam + mirrored/bordered images + flash; the vertical
 tier 1080×1920 crop/scale), StretchMathTests (UniformToFill cover-crop + bilinear), FfmpegLocatorTests
 (the PATH → cache → download decision ladder with a fake downloader serving a real in-memory zip; shared
 build DLL extraction) —
@@ -134,13 +152,30 @@ C# / WPF (.NET 8) following MVVM:
 - `StreamConfig` defaults (`TargetBitrate=6000`, `Resolution="1920x1080"`) are stale — the live dropdown drives `StreamHealth.CurrentBitrate`/`FPS` instead
 - **v1 task queue (2026-08-19):** tasks 19-23 added for v1 feature completeness; TASK 3.18 (chat box) shipped; TASK 16 (infinity display) shipped; TASK 10 (Polar billing) shipped — steps 1-7 (Velopack bootstrap, PolarLicenseService, license entry UI, LayoutStore entitlement, BrandFlash toggle, startup re-validation, PremiumUrl wired); Velopack update URL pending:
   - TASK 10: Polar billing — license key entry, offline entitlement, brand flash gating, Velopack auto-updates
-  - TASK 19: Scene transitions (Cut/Fade/Move/Custom) — required for professional polish
+  - TASK 19/23 merged: Control Surface UX — director's control room, transitions (Cut/Fade/Move), thumbnails above central monitor, edit mode offline only, right panel eliminated
   - TASK 20: Hotkeys (global keyboard shortcuts) — the single biggest UX gap
   - TASK 21: Media source (video file playback) — starting soon videos, BRB loops
   - TASK 22: Audio sync offset — lip-sync correction for USB mics/capture cards
-  - TASK 23: Studio mode (lightweight preview) — preview next scene before live
   - These were identified through competitive analysis and are table-stakes for any streaming software in 2025-2026. Full details in `TASKS.md`.
 
+### Control Surface UX (TASK 19/23 merged — active)
+
+The app is a **director's control surface**, not an editor. This replaces the OBS-style scene list with a TV-control-room metaphor.
+
+**Layout:** Two-column. Left panel = one panel, two states. Center = thumbnails above central monitor.
+
+- **Left panel:** When offline (edit mode) → LAYERS + PROPERTIES (same as current, minus SCREENS). When live/recording → YouTube Live Chat (entire panel replaced, never coexists with layers/properties). Mode is implicit (derived from `StreamStatus`), no toggle button.
+- **Thumbnails:** Five scene previews above the central monitor, 16:9, drag-reorderable. Click = stage (offline) or transition (live). Active scene gets brand-red glow border.
+- **Central monitor:** Shows staged scene (offline, editable in edit mode) or live output (live, read-only). During transitions: compositor-blended animation.
+- **Right panel:** Eliminated. Chat moved to left panel (live mode).
+- **Edit gating:** `IsEditMode` = `StreamStatus == Offline`. When live/recording: all drag/resize, context menus, right-click property adjustments disabled. Gun safety — no accidental edits mid-stream.
+
+**Scene reference split:** `ActiveScene` → `StagedScene` (central monitor target, editable offline) + `LiveScene` (encoder output). Go Live sets `LiveScene = StagedScene`. Thumbnail click sets `StagedScene` (offline) or fires transition (live).
+
+**Transitions:** `TransitionService` (new file) — Cut/Fade/Move with configurable duration (default 300ms). `SceneCompositor.RenderBlend()` blends two scenes' frames. `FramePump` feeds `LiveScene` to encoder; during transitions, feeds blended frames. Go Live always = Cut (clean start).
+
+**Thumbnails:** `Scene.Snapshot` property. `SceneCompositor.Render()` at 320×180 → `WriteableBitmap`. Only staged scene has live backdrop render; other 4 = static snapshots.
+
 ### Screen backdrop capture (TASK 3 ship task #1)
 
 The backdrop is the **live desktop/game capture as a permanent, non-deletable bottom layer**