Optimize KC processing and add reactive HAOS state updates

- Optimize KC frame processing: downsample to 160x90 with cv2.resize
  before rectangle extraction, pre-compute pixel coords, vectorize
  smoothing with numpy arrays
- Add WebSocket event stream for server state changes: processor manager
  fires events on start/stop, new /api/v1/events/ws endpoint streams
  them to connected clients
- Add HAOS EventStreamListener that triggers coordinator refresh on
  state changes for near-instant switch updates
- Reduce HAOS polling interval from 10s to 3s for fresher FPS metrics
- Fix overlay button tooltips: flatten nested JSON keys in locale files
  to match flat dot-notation lookup used by t() function

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/wled_controller/static/locales/en.json

@@ -440,16 +440,10 @@
   "pattern.description.hint": "Optional notes about where or how this pattern is used",
   "pattern.visual_editor.hint": "Click + buttons to add rectangles. Drag edges to resize, drag inside to move.",
   "pattern.rectangles.hint": "Fine-tune rectangle positions and sizes with exact coordinates (0.0 to 1.0)",
-  "overlay": {
-    "button": {
-      "show": "Show overlay visualization",
-      "hide": "Hide overlay visualization"
-    },
-    "started": "Overlay visualization started",
-    "stopped": "Overlay visualization stopped",
-    "error": {
-      "start": "Failed to start overlay",
-      "stop": "Failed to stop overlay"
-    }
-  }
+  "overlay.button.show": "Show overlay visualization",
+  "overlay.button.hide": "Hide overlay visualization",
+  "overlay.started": "Overlay visualization started",
+  "overlay.stopped": "Overlay visualization stopped",
+  "overlay.error.start": "Failed to start overlay",
+  "overlay.error.stop": "Failed to stop overlay"
 }