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/tests/conftest.py

@@ -1,10 +1,6 @@
 """Pytest configuration and shared fixtures."""
 
-import json
-import os
 from datetime import datetime, timezone
-from pathlib import Path
-from unittest.mock import AsyncMock, MagicMock
 
 import pytest
 
@@ -15,11 +11,8 @@ from wled_controller.storage.sync_clock_store import SyncClockStore
 from wled_controller.storage.output_target_store import OutputTargetStore
 from wled_controller.storage.automation import (
     Automation,
-    AlwaysCondition,
-    WebhookCondition,
 )
 from wled_controller.storage.automation_store import AutomationStore
-from wled_controller.storage.value_source import StaticValueSource, ValueSource
 from wled_controller.storage.value_source_store import ValueSourceStore