Optimize numpy pipeline, add per-stage timing, and auto-sync LED count

- Eliminate 5 numpy↔tuple conversions per frame in processing hot path:
  map_border_to_leds returns ndarray, inline numpy smoothing with integer
  math, send_pixels_fast accepts ndarray directly
- Fix numpy boolean bug in keepalive check (use `is not None`)
- Add per-stage pipeline timing (extract/map/smooth/send) to metrics API
  and UI with color-coded breakdown bar
- Expose device_fps from WLED health check in API schemas
- Auto-sync LED count from WLED device: health check detects changes and
  updates storage, calibration, and active targets automatically
- Use integer math for brightness scaling (uint16 * brightness >> 8)

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

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

@@ -150,6 +150,8 @@
   "device.metrics.frames_skipped": "Skipped",
   "device.metrics.keepalive": "Keepalive",
   "device.metrics.errors": "Errors",
+  "device.metrics.timing": "Pipeline timing:",
+  "device.metrics.device_fps": "Device refresh rate",
   "device.health.online": "Online",
   "device.health.offline": "Offline",
   "device.health.checking": "Checking...",