feat(setup): separate NFO scan into dedicated phase

- Add /nfo-scan-phase endpoint to trigger NFO scan independently
- Move NFO scan out of initial setup into separate post-unresolved phase
- Add phase query param handling for /loading page (?phase=initial, ?phase=nfo)
- Update setup redirect middleware to handle phase-based redirects
- Update auth setup to pass phase=initial to loading page

src/server/api/auth.py

@@ -208,8 +208,9 @@ async def setup_auth(req: SetupRequest):
         # Start initialization in background
         asyncio.create_task(run_initialization())
         
-        # Return redirect to loading page
-        return {"status": "ok", "redirect": "/loading"}
+        # Return redirect to loading page with phase=initial
+        # The loading page will show ONLY series_sync step, then redirect to /setup/unresolved
+        return {"status": "ok", "redirect": "/loading?phase=initial"}
         # Note: Media scan is skipped during setup as it requires
         # background_loader service which is only available during
         # application lifespan. It will run on first application startup.