refactor(scheduler): replace structlog with std logging and add extensive diagnostics

- Switch scheduler_service from structlog to standard logging for consistency
- Add detailed lifecycle logging in SchedulerService (start, stop, rescan)
- Add debug logging in fastapi_app scheduler initialization
- Fix test_add_series_episodes to mock EpisodeService.get_by_series

src/server/fastapi_app.py

@@ -121,7 +121,7 @@ async def _run_startup_health_checks(logger) -> dict:
     import asyncio
     import shutil
     import socket
-    from typing import Dict, Any
+    from typing import Any, Dict
     
     checks: Dict[str, Any] = {
         "ffmpeg": {"status": "unknown", "message": None},
@@ -400,13 +400,15 @@ async def lifespan(_application: FastAPI):
 
                 # Initialize and start scheduler service
                 try:
+                    logger.info("Initializing scheduler service...")
                     from src.server.services.scheduler_service import (
                         get_scheduler_service,
                     )
                     scheduler_service = get_scheduler_service()
+                    logger.info("Scheduler service instance obtained, starting...")
                     await scheduler_service.start()
                     initialized['scheduler'] = True
-                    logger.info("Scheduler service started")
+                    logger.info("Scheduler service started successfully")
                 except Exception as e:
                     logger.warning("Failed to start scheduler service: %s", e)
                     # Continue - scheduler is optional