offroad UI: replace stock home with clean grid launcher

- Strip out date, version, update/alert widgets from OffroadHome
- Replace with grid layout: Dashcam and Settings buttons
- Skip sidebar when tapping splash screen
- Settings button still opens original comma settings
- Dashcam button placeholder (viewer not yet built)
- Add DASHCAM_PROJECT.md with plans for footage viewer

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

DASHCAM_PROJECT.md

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+# Dashcam Project
+
+## Status
+
+### Completed (2026-04-11)
+
+- Disabled comma training data video encoding (`encoderd`) — CAN/sensor logs still recorded
+- Re-enabled FrogPilot OMX screen recorder (H.264 MP4, 1440x720, 2Mbps, hardware encoded)
+- Auto-start/stop recording tied to car ignition (`scene.started`)
+- `ScreenRecorderDebug` param for bench testing without car connected
+- Hidden all recorder UI elements — invisible to driver
+- Videos saved to `/data/media/0/videos/YYYYMMDD-HHMMSS.mp4`, 3-minute segments
+- Deleter updated: 9 GB free space threshold, rotates oldest videos first
+- Cleaned up offroad UI: replaced stock home screen with grid launcher (Settings + Dashcam buttons)
+
+### Next: Dashcam Footage Viewer
+
+Build a native Qt widget accessible from the offroad home screen "Dashcam" button.
+
+**Requirements:**
+- List MP4 files from `/data/media/0/videos/` sorted newest first
+- Tap a file to play it back using Qt Multimedia (`QMediaPlayer` + `QVideoWidget`)
+- Only accessible when offroad (car in park or off)
+- Back button to return to offroad home
+- No rotation hacks needed — native Qt widget in existing UI tree handles rotation correctly
+
+**Architecture:**
+- New widget class (e.g. `DashcamViewer`) added to `selfdrive/ui/qt/`
+- Wire into `HomeWindow`'s `QStackedLayout` alongside `home`, `onroad`, `ready`, `driver_view`
+- Dashcam button in `OffroadHome` switches `slayout` to the viewer
+- Viewer has a file list view and a playback view (sub-stacked layout)
+- Back button returns to `OffroadHome`
+- Build: add to `qt_src` list in `selfdrive/ui/SConscript`, link `Qt5Multimedia`
+
+**Previous webview attempts (abandoned):**
+- Brian tried QWebEngineView for browser-based playback but the WebEngine subprocess renders independently of Qt's widget tree
+- Screen rotation (`view.rotate(90)`, Wayland `wl_surface_set_buffer_transform`) did not work for WebEngine content
+- Native Qt widget approach avoids this problem entirely
+
+## Key Files
+
+| File | Role |
+|------|------|
+| `selfdrive/frogpilot/screenrecorder/screenrecorder.cc` | Recording logic, auto-start/stop |
+| `selfdrive/frogpilot/screenrecorder/omx_encoder.cc` | OMX H.264 hardware encoder |
+| `selfdrive/ui/qt/onroad.cc` | Timer driving frame capture |
+| `selfdrive/ui/qt/home.cc` | Offroad home with Dashcam button |
+| `system/loggerd/deleter.py` | Storage rotation |
+| `/data/media/0/videos/` | Video output directory |