refactor(scheduler): separate scheduler logic from scan/rescan logic

- Extract rescan logic into new RescanService (src/server/services/rescan_service.py)
- SchedulerService now only handles APScheduler cron scheduling
- Move scheduler sub-services (folder_rename, folder_scan, key_resolution) to scheduler/ folder
- Keep RescanOrchestrator as backward-compatible alias
- Update all imports across api/, server/, and test files

tests/integration/test_scheduler_workflow.py

@@ -11,15 +11,14 @@ from unittest.mock import AsyncMock, Mock, patch
 import pytest
 
 from src.server.models.config import AppConfig, SchedulerConfig
-from src.server.services.scheduler_service import (
+from src.server.services.scheduler.scheduler_service import (
+    _JOB_ID,
     SchedulerService,
     SchedulerServiceError,
-    _JOB_ID,
     get_scheduler_service,
     reset_scheduler_service,
 )
 
-
 # ---------------------------------------------------------------------------
 # Shared fixtures
 # ---------------------------------------------------------------------------
@@ -27,7 +26,7 @@ from src.server.services.scheduler_service import (
 @pytest.fixture
 def mock_config_service():
     """Patch get_config_service used by SchedulerService.start()."""
-    with patch("src.server.services.scheduler_service.get_config_service") as mock:
+    with patch("src.server.services.scheduler.scheduler_service.get_config_service") as mock:
         config_service = Mock()
         app_config = AppConfig(
             scheduler=SchedulerConfig(