fix: dashcamd OMX crash on restart, add dashcam status indicator

- Reset OMX subsystem (Deinit/Init) on dashcamd startup to clear stale
  encoder state from previous unclean exits
- Validate OMX output buffers before memcpy to prevent segfault
- Validate VisionBuf frame data before encoding
- Add dashcam row to status window showing recording state and disk usage

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

selfdrive/ui/qt/window.h

@@ -20,6 +20,7 @@ public:
   struct StatusData {
     QString time, storage, ram, load, temp, fan, ip, wifi;
     QString vpn_status, vpn_ip, gps, telemetry;
+    QString dashcam_status, dashcam_size;
     float temp_c = 0;
   };
 
@@ -49,6 +50,7 @@ private:
   QLabel *gps_label;
   QLabel *time_label;
   QLabel *telemetry_label;
+  QLabel *dashcam_label;
   QLabel *panda_label;
 };