fix(scheduler): skip rescan during initial setup when anime directory not configured

Prevent scheduler from triggering immediate rescan when:
- No previous scan recorded AND initial setup not yet completed
- Anime directory doesn't exist during initial sync

The setup flow will trigger rescan when ready. Also adds graceful
handling when anime directory is missing during data file sync.

Fixes: 503 error on setup when scheduler triggers rescan before
anime directory is configured

src/server/services/scheduler/scheduler_service.py

@@ -323,8 +323,18 @@ class SchedulerService:
             async with get_db_session() as db:
                 settings = await SystemSettingsService.get_or_create(db)
                 last_scan = settings.last_scan_timestamp
+                initial_scan_done = settings.initial_scan_completed
 
             if last_scan is None:
+                # No previous scan recorded
+                if not initial_scan_done:
+                    # Initial setup not yet completed - skip rescan
+                    # The setup flow will trigger rescan when ready
+                    logger.info(
+                        "No previous scan recorded and initial setup not yet "
+                        "completed — skipping immediate rescan"
+                    )
+                    return
                 # Never scanned before — trigger immediately
                 logger.info("No previous scan recorded — triggering immediate rescan")
                 await self._perform_rescan()