Add camera/webcam capture engine with engine-aware display picker

- New CameraEngine using OpenCV VideoCapture for webcam capture
- HAS_OWN_DISPLAYS class attribute on CaptureEngine base to distinguish
  engines with their own device lists from desktop monitor engines
- Display picker renders device list for cameras/scrcpy, spatial layout
  for desktop monitors
- Engine-aware display label formatting (camera name vs monitor index)
- Stream modal properly loads engine-specific displays on template change,
  edit, and clone
- Camera backend config rendered as dropdown (auto/dshow/msmf/v4l2)
- Remove offline label from device cards (healthcheck indicator suffices)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

TODO.md

@@ -20,9 +20,7 @@ Priority: `P1` quick win · `P2` moderate · `P3` large effort
 - [ ] `P1` **Rename `picture-targets` to `output-targets`** — Rename API endpoints and internal references for clarity
   - Complexity: low — mechanical rename across routes, schemas, store, frontend fetch calls; no logic changes, but many files touched (~20+), needs care with stored JSON migration
   - Impact: low-medium — improves API clarity for future integrations (OpenRGB, Art-Net)
-- [ ] `P2` **OpenRGB** — Control PC peripherals (keyboard, mouse, RAM, fans) as ambient targets
-  - Complexity: medium — new device type + client (OpenRGB SDK uses a TCP socket protocol); new target processor subclass; device discovery via OpenRGB server
-  - Impact: high — extends ambient lighting beyond WLED to entire PC ecosystem
+- [x] `P2` **OpenRGB** — Control PC peripherals (keyboard, mouse, RAM, fans) as ambient targets
 - [ ] `P2` **Art-Net / sACN (E1.31)** — Stage/theatrical lighting protocols, DMX controllers
   - Complexity: medium — UDP-based protocols with well-documented specs; similar architecture to DDP client; needs DMX universe/channel mapping UI
   - Impact: medium — opens stage/theatrical use case, niche but differentiating
@@ -53,12 +51,13 @@ Priority: `P1` quick win · `P2` moderate · `P3` large effort
 - [ ] `P3` **SCRCPY capture engine** — Implement SCRCPY-based screen capture for Android devices
   - Complexity: large — external dependency on scrcpy binary; need to manage subprocess lifecycle, parse video stream (ffmpeg/AV pipe), handle device connect/disconnect
   - Impact: medium — enables phone screen mirroring to ambient lighting; appeals to mobile gaming use case
-- [ ] `P3` **Camera / webcam** — Border-sampling from camera feed for video calls or room-reactive lighting
-  - Complexity: medium — OpenCV `VideoCapture` is straightforward; needs new capture source type + calibration for camera field of view; FPS/resolution config
-  - Impact: low-medium — room-reactive lighting is novel but limited practical appeal
+- [x] `P3` **Camera / webcam** — Border-sampling from camera feed for video calls or room-reactive lighting
 
 ## UX
 
+- [ ] `P2` **Tags / groups for cards** — Assign tags to devices, targets, and sources; filter and group cards by tag
+  - Complexity: medium — new `tags: List[str]` field on all card entities; tag CRUD API; filter bar UI per section; tag badge rendering on cards; persistence migration
+  - Impact: medium-high — essential for setups with many devices/targets; enables quick filtering (e.g. "bedroom", "desk", "gaming")
 - [ ] `P3` **PWA / mobile layout** — Mobile-first layout + "Add to Home Screen" manifest
   - Complexity: medium-large — responsive CSS overhaul for all tabs; service worker for offline caching; manifest.json; touch-friendly controls (larger tap targets, swipe gestures)
   - Impact: high — phone control is a top user request; current desktop-first layout is unusable on mobile