Animation None option, FPS min 1, serial COM lifecycle fixes

- Replace animation Enable checkbox with None option in effect selector;
  show effect description tooltip; disable speed slider when None selected
- Allow target FPS range 1-90 (was 10-90) across UI and backend validation
- Scope serial COM connections to target lifetime (no idle caching);
  use temporary connections for power-off/test mode
- Fix serial black frame on stop: flush after write, delay after task
  cancel to prevent race with in-flight thread pool write

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

server/src/wled_controller/core/devices/adalight_client.py

@@ -105,9 +105,22 @@ class AdalightClient(LEDClient):
             try:
                 black = np.zeros((self._led_count, 3), dtype=np.uint8)
                 frame = self._build_frame(black, brightness=255)
+                logger.info(
+                    f"Adalight sending black frame: {self._port} "
+                    f"({self._led_count} LEDs, {len(frame)} bytes)"
+                )
                 await asyncio.to_thread(self._serial.write, frame)
+                await asyncio.to_thread(self._serial.flush)
+                logger.info(f"Adalight black frame sent and flushed: {self._port}")
             except Exception as e:
-                logger.debug(f"Failed to send black frame on close: {e}")
+                logger.warning(f"Failed to send black frame on close: {e}")
+        else:
+            logger.warning(
+                f"Adalight close skipped black frame: port={self._port} "
+                f"connected={self._connected} serial={self._serial is not None} "
+                f"is_open={self._serial.is_open if self._serial else 'N/A'} "
+                f"led_count={self._led_count}"
+            )
         self._connected = False
         if self._serial and self._serial.is_open:
             try: