Add re-order, spotlight/focus, and auto-position-snapshots features

- HTML5 drag-and-drop reordering of strip participants (per-GM flag)
- Shift+click toggles spotlight focus on a participant (gold ring indicator)
- Escape exits focus mode
- Auto-save strip position on drag end + every 30s with viewport validation
- Reset strip position button in Director's Board
- French locale strings for reset button

lang/en.json

@@ -79,7 +79,8 @@
         "avModeEnable": "Enable A/V",
         "avModeDisable": "Disable A/V",
         "avConfig": "A/V Settings…",
-        "avConfigTitle": "Open Foundry A/V server settings (signaling server, LiveKit, etc.)"
+        "avConfigTitle": "Open Foundry A/V server settings (signaling server, LiveKit, etc.)",
+        "resetStrip": "Reset Strip Position"
       },
       "bulk": {
         "showAll": "Show All",