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/storage/color_strip_store.py

@@ -2,26 +2,15 @@
 
 import uuid
 from datetime import datetime, timezone
-from typing import List, Optional
+from typing import List
 
 from wled_controller.storage.base_store import BaseJsonStore
 from wled_controller.storage.utils import resolve_ref
 from wled_controller.storage.color_strip_source import (
-    AdvancedPictureColorStripSource,
-    ApiInputColorStripSource,
-    AudioColorStripSource,
-    CandlelightColorStripSource,
-    ColorCycleColorStripSource,
     ColorStripSource,
     CompositeColorStripSource,
-    DaylightColorStripSource,
-    EffectColorStripSource,
-    GradientColorStripSource,
     MappedColorStripSource,
-    NotificationColorStripSource,
-    PictureColorStripSource,
     ProcessedColorStripSource,
-    StaticColorStripSource,
 )
 from wled_controller.utils import get_logger
 

server/src/wled_controller/storage/device_store.py

@@ -4,7 +4,7 @@ import json
 import uuid
 from datetime import datetime, timezone
 from pathlib import Path
-from typing import Dict, List, Optional
+from typing import List, Optional
 
 from wled_controller.storage.base_store import BaseJsonStore
 from wled_controller.utils import get_logger

server/src/wled_controller/storage/key_colors_output_target.py

@@ -2,7 +2,6 @@
 
 from dataclasses import dataclass, field
 from datetime import datetime, timezone
-from typing import List, Optional
 
 from wled_controller.storage.output_target import OutputTarget
 from wled_controller.storage.utils import resolve_ref

server/src/wled_controller/storage/output_target_store.py

@@ -1,6 +1,5 @@
 """Output target storage using JSON files."""
 
-import json
 import uuid
 from datetime import datetime, timezone
 from typing import List, Optional