fix(videos): set explicit 4Mbps bitrate for hw encode

Default h264_v4l2m2m bitrate was ~200kbps producing unusable quality.
4M video + 128k audio = ~100MB per 3-min clip, proper dashcam quality.

Co-authored-by: Copilot <[email protected]>

modules/app_video.py

@@ -62,7 +62,9 @@ def _convert_bg(relative_path):
                 "ffmpeg", "-nostdin", "-loglevel", "error", "-y",
                 "-i", source_path,
                 "-c:v", "h264_v4l2m2m",
+                "-b:v", "4M",        # 4 Mbps — good quality, ~100MB per 3-min clip
                 "-c:a", "aac",
+                "-b:a", "128k",
                 "-movflags", "faststart",
                 "-f", "mp4",
                 tmp_path,