Fix scheduler next_run_time None check; add debug logging

- Fix race condition: next_run_time only available after scheduler.start()
- Handle None gracefully in logging
- Add debug logging to _perform_rescan and _run_rescan_job
- Document scheduler troubleshooting in DEVELOPMENT.md

docs/DEVELOPMENT.md

@@ -231,6 +231,50 @@ DNS checks are warnings because failures can be transient. anime_directory error
 5. Monitor next run: `GET /health` → `scheduler_next_run`
 6. If problem repeats, increase `misfire_grace_time` in `scheduler_service.py`.
 
+#### Scheduler not firing (no events at scheduled time)
+
+If the scheduler appears configured but never triggers:
+
+1. **Verify scheduler.db contains the job:**
+   ```bash
+   sqlite3 data/scheduler.db "SELECT id, next_run_time FROM apscheduler_jobs;"
+   ```
+   - `next_run_time` should be in the future
+   - If it's in the past, the server was down when the job should have fired
+
+2. **Check application logs for scheduler startup:**
+   ```
+   grep "Scheduler service started" fastapi_app.log
+   ```
+   - If missing, the scheduler failed to start — check for errors above this line
+   - If present, scheduler started successfully
+
+3. **Verify APScheduler events in logs:**
+   ```
+   grep "apscheduler.executors.default" fastapi_app.log
+   ```
+   - `Running job` = job triggered
+   - `executed successfully` = job completed
+   - No output = job never fired
+
+4. **Test manual trigger:**
+   ```bash
+   curl -X POST http://localhost:8000/api/scheduler/trigger-rescan -H "Authorization: Bearer <token>"
+   ```
+   - If manual trigger works but cron doesn't, the issue is APScheduler configuration
+
+5. **Check next_run_time via health endpoint:**
+   ```bash
+   curl http://localhost:8000/health | jq .scheduler_next_run
+   ```
+   - If `null`, the job is not scheduled
+   - If set, the scheduler knows when to run next
+
+6. **Check timezone handling:**
+   - APScheduler uses UTC internally
+   - The schedule_time config (e.g., "03:00") is interpreted as UTC
+   - If you expect local time, adjust the schedule_time accordingly
+
 #### Startup health check failures
 
 If `/health` returns `unhealthy` status: