crop motion previews to the selected filter region (#23903)

When a motion region filter is active, zoom each preview clip into the outer bounds of the selected cells instead of showing the full frame. Tiles take on the aspect ratio of the cropped region, clamped to avoid slivers when the selection is a single row or column, so the grid stays uniform. A "Crop to filter" switch in the preview settings turns this off and restores the previous 16:9 tiles. The transform is applied to a wrapper holding both the media and the dim overlay canvas so the motion heatmap stays registered to the pixels.

Fix the region filter grid, which mapped cells onto a hardcoded 16:9 box while the snapshot was letterboxed inside it with object-contain. Heatmap cells are indexed against the detect frame, so on a 4:3 camera every painted cell was off by up to 12.5% of the frame width, and the true left and right edges of the image could only be reached by painting the black bars. The grid box now takes the camera's detect aspect ratio, capped at 65dvh tall so 4:3 and portrait cameras do not overflow the dialog.

web/public/locales/en/views/events.json

@@ -74,7 +74,7 @@
     "menuItem": "View motion previews",
     "title": "Motion previews: {{camera}}",
     "mobileSettingsTitle": "Motion Preview Settings",
-    "mobileSettingsDesc": "Adjust playback speed and dimming, and choose a date to review motion-only clips.",
+    "mobileSettingsDesc": "Adjust playback speed, dimming, and cropping, and choose a date to review motion-only clips.",
     "dim": "Dim",
     "dimAria": "Adjust dimming intensity",
     "dimDesc": "Increase dimming to increase motion area visibility.",
@@ -87,6 +87,9 @@
     "seekAria": "Seek {{camera}} player to {{time}}",
     "filter": "Filter",
     "filterDesc": "Select areas to only show clips with motion in those regions.",
-    "filterClear": "Clear"
+    "filterClear": "Clear",
+    "crop": "Crop to filter",
+    "cropAria": "Toggle cropping previews to the filtered areas",
+    "cropDesc": "Zoom previews into the selected filter areas instead of showing the full frame."
   }
 }