feat(dashcam): mobile layout fix + optional hw-encode conversion on import

- yaris.css: on mobile (<576px) hide file/size/date/upload cols, show
  filename inside thumb cell, icon-only buttons, dash-actions-td nowrap
- local-videos.js: filename in thumb cell for mobile; Converting badge with
  spinner; auto-refresh every 10s while any file is converting
- app_video.py: CONVERT_SETTING, is_convert_enabled(), queue_convert(),
  _convert_bg() — h264_v4l2m2m + aac faststart, deletes original on success
- app_dash.py: call queue_convert() after each successful copy on import
- app_settings.py: expose video_convert_enabled in get/save settings
- settings.html: toggle for 'Convert imported videos for web playback'

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

templates/settings.html

@@ -39,6 +39,13 @@
                 <span class="small text-muted">(0 = keep forever)</span>
             </div>
             <div class="invalid-feedback" data-error-for="local_video_retention_days"></div>
+            <div class="form-check form-switch mt-3">
+                <input class="form-check-input" type="checkbox" role="switch" id="video-convert-enabled">
+                <label class="form-check-label" for="video-convert-enabled">
+                    Convert imported videos for web playback
+                    <span class="text-muted small d-block">Re-encodes MOV→MP4 using hardware encoder in background after import. Original deleted when done.</span>
+                </label>
+            </div>
         </div>
     </div>