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/dependencies.py

@@ -4,7 +4,7 @@ Uses a registry dict instead of individual module-level globals.
 All getter function signatures remain unchanged for FastAPI Depends() compatibility.
 """
 
-from typing import Any, Dict, Type, TypeVar
+from typing import Any, Dict, TypeVar
 
 from wled_controller.core.processing.processor_manager import ProcessorManager
 from wled_controller.storage import DeviceStore