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/unit/test_scheduler_service.py

@@ -15,7 +15,7 @@ import pytest
 from apscheduler.triggers.cron import CronTrigger
 
 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,
@@ -36,7 +36,7 @@ def _make_app_config(**scheduler_kwargs) -> AppConfig:
 
 @pytest.fixture
 def mock_config_service():
-    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:
         svc = Mock()
         svc.load_config.return_value = _make_app_config(
             enabled=True,
@@ -105,7 +105,7 @@ class TestStart:
         self, scheduler_service, mock_config_service
     ):
         with patch(
-            "src.server.services.scheduler_service.AsyncIOScheduler"
+            "src.server.services.scheduler.scheduler_service.AsyncIOScheduler"
         ) as MockScheduler:
             mock_sched = MagicMock()
             mock_sched.running = False
@@ -137,9 +137,9 @@ class TestStartEmptyDays:
     @pytest.mark.asyncio
     async def test_no_job_added_when_days_empty(self, scheduler_service):
         with patch(
-            "src.server.services.scheduler_service.get_config_service"
+            "src.server.services.scheduler.scheduler_service.get_config_service"
         ) as mock_cs, patch(
-            "src.server.services.scheduler_service.AsyncIOScheduler"
+            "src.server.services.scheduler.scheduler_service.AsyncIOScheduler"
         ) as MockScheduler:
             svc = Mock()
             svc.load_config.return_value = _make_app_config(
@@ -409,7 +409,7 @@ class TestPerformRescanFolderScan:
 
         with patch("src.server.utils.dependencies.get_anime_service", return_value=mock_anime), \
              patch("src.server.services.websocket_service.get_websocket_service", return_value=mock_ws), \
-             patch("src.server.services.folder_scan_service.FolderScanService") as MockFSS:
+             patch("src.server.services.scheduler.folder_scan_service.FolderScanService") as MockFSS:
             MockFSS.return_value.run_folder_scan = mock_folder_scan
             await scheduler_service._perform_rescan()
 
@@ -434,7 +434,7 @@ class TestPerformRescanFolderScan:
 
         with patch("src.server.utils.dependencies.get_anime_service", return_value=mock_anime), \
              patch("src.server.services.websocket_service.get_websocket_service", return_value=mock_ws), \
-             patch("src.server.services.folder_scan_service.FolderScanService") as MockFSS:
+             patch("src.server.services.scheduler.folder_scan_service.FolderScanService") as MockFSS:
             MockFSS.return_value.run_folder_scan = mock_folder_scan
             await scheduler_service._perform_rescan()
 
@@ -459,7 +459,7 @@ class TestPerformRescanFolderScan:
 
         with patch("src.server.utils.dependencies.get_anime_service", return_value=mock_anime), \
              patch("src.server.services.websocket_service.get_websocket_service", return_value=mock_ws), \
-             patch("src.server.services.folder_scan_service.FolderScanService") as MockFSS:
+             patch("src.server.services.scheduler.folder_scan_service.FolderScanService") as MockFSS:
             MockFSS.return_value.run_folder_scan = mock_folder_scan
             # Should NOT raise
             await scheduler_service._perform_rescan()
@@ -498,7 +498,7 @@ class TestInMemoryJobStore:
         self, scheduler_service, mock_config_service
     ):
         with patch(
-            "src.server.services.scheduler_service.AsyncIOScheduler"
+            "src.server.services.scheduler.scheduler_service.AsyncIOScheduler"
         ) as MockScheduler:
             mock_sched = MagicMock()
             mock_sched.running = False
@@ -517,7 +517,7 @@ class TestInMemoryJobStore:
         self, scheduler_service, mock_config_service
     ):
         with patch(
-            "src.server.services.scheduler_service.AsyncIOScheduler"
+            "src.server.services.scheduler.scheduler_service.AsyncIOScheduler"
         ) as MockScheduler:
             mock_sched = MagicMock()
             mock_sched.running = False
@@ -540,7 +540,7 @@ class TestStartupRecovery:
         self, scheduler_service, mock_config_service
     ):
         with patch(
-            "src.server.services.scheduler_service.AsyncIOScheduler"
+            "src.server.services.scheduler.scheduler_service.AsyncIOScheduler"
         ) as MockScheduler:
             mock_job = MagicMock()
             next_run_dt = datetime(2026, 5, 25, 3, 0, tzinfo=timezone.utc)
@@ -551,7 +551,7 @@ class TestStartupRecovery:
             MockScheduler.return_value = mock_sched
 
             with patch(
-                "src.server.services.scheduler_service.logger"
+                "src.server.services.scheduler.scheduler_service.logger"
             ) as mock_logger:
                 await scheduler_service.start()
                 info_calls = [str(c) for c in mock_logger.info.call_args_list]