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/utils/monitor_names.py

@@ -1,7 +1,7 @@
 """Utility functions for retrieving friendly monitor/display names."""
 
 import sys
-from typing import Dict, Optional
+from typing import Dict
 
 from wled_controller.utils import get_logger
 
@@ -129,7 +129,7 @@ def get_monitor_refresh_rates() -> Dict[int, int]:
         # Enumerate all display devices
         idx = 0
         while True:
-            device_name = ctypes.create_unicode_buffer(32)
+            ctypes.create_unicode_buffer(32)
             if not user32.EnumDisplayDevicesW(None, idx, None, 0):
                 # Try getting display settings by index
                 devmode = DEVMODE()