test(integration): Add comprehensive migration integration tests (Task 8)

Task 8: Write integration tests for data file migration
- Added test_migration_on_fresh_start_no_data_files test
- Added test_add_series_saves_to_database test
- Added test_scan_async_saves_to_database test
- Added test_load_series_from_db test
- Added test_search_and_add_workflow test
- All 11 migration integration tests pass
- All 870 tests pass (815 unit + 55 API)

data/config.json

@@ -17,7 +17,7 @@
     "keep_days": 30
   },
   "other": {
-    "master_password_hash": "$pbkdf2-sha256$29000$3rvXWouRkpIyRugdo1SqdQ$WQaiQF31djFIKeoDtZFY1urJL21G4ZJ3d0omSj5Yark",
+    "master_password_hash": "$pbkdf2-sha256$29000$JGRMCcHY.9.7d24tJQQAAA$pzRSDd4nRdLzzB/ZhSmFoENCwyn9K43tqvRwq6SNeGA",
     "anime_directory": "/mnt/server/serien/Serien/"
   },
   "version": "1.0.0"

data/download_queue.json

@@ -2,5 +2,5 @@
   "pending": [],
   "active": [],
   "failed": [],
-  "timestamp": "2025-12-01T18:41:52.350980+00:00"
+  "timestamp": "2025-12-01T18:47:07.269087+00:00"
 }