fix: resolve all 153 ruff lint errors for CI

Auto-fixed 138 unused imports and f-string issues. Manually fixed:
ambiguous variable names (l→layer), availability-check imports using
importlib.util.find_spec, unused Color import, ImagePool forward ref
via TYPE_CHECKING, multi-statement semicolons, and E402 suppression.

server/src/wled_controller/api/routes/output_targets_control.py

@@ -3,15 +3,12 @@
 Extracted from output_targets.py to keep files under 800 lines.
 """
 
-import asyncio
 
 from fastapi import APIRouter, HTTPException, Depends, Query, WebSocket, WebSocketDisconnect
 
 from wled_controller.api.auth import AuthRequired
 from wled_controller.api.dependencies import (
-    fire_entity_event,
     get_color_strip_store,
-    get_device_store,
     get_output_target_store,
     get_picture_source_store,
     get_processor_manager,