Story 5.2: Video Widget Width Customization

Implements configurable video widget widths for small and large dock layouts:
- Add widgetWidthSm and widgetWidthMd world settings (defaults: 83px, 150px)
- Add width dropdown selectors in Director's Board UI
- Apply width settings to participant avatars via CSS custom properties
- Update strip width/height calculations to use custom widths
- Add localization strings for widget width settings
- Add CSS styling for widget width dropdown controls
- Fix Handlebars template syntax for select element selected values

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

lang/en.json

@@ -58,6 +58,11 @@
         "mosaic-sm": "Mosaic Small",
         "mosaic-md": "Mosaic Large"
       },
+      "widgetWidth": {
+        "label": "Video Widget Widths",
+        "small": "Small:",
+        "large": "Large:"
+      },
       "footer": {
         "savePreset": "Save Layout",
         "loadPreset": "Load Layout",