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/setup_endpoints.py

@@ -373,4 +373,51 @@ async def complete_unresolved_folders(
         status="success",
         message=f"Marked {count} folders as handled. Unresolved phase completed.",
         count=count,
+    )
+
+
+class NfoScanPhaseResponse(BaseModel):
+    """Response model for NFO scan phase trigger."""
+    status: str = Field(..., description="Status of the operation")
+    message: str = Field(..., description="Human-readable message")
+
+
+@router.post("/nfo-scan-phase", response_model=NfoScanPhaseResponse)
+async def trigger_nfo_scan_phase() -> NfoScanPhaseResponse:
+    """Trigger the NFO scan phase.
+    
+    This endpoint is called by the loading page when accessed with ?phase=nfo.
+    It starts the NFO scan in the background and returns immediately.
+    The loading page then connects via WebSocket to receive progress updates.
+    
+    Returns:
+        NfoScanPhaseResponse with status and message
+    """
+    import asyncio
+
+    from src.server.services.initialization_service import perform_nfo_scan_phase
+    from src.server.services.progress_service import get_progress_service
+    
+    progress_service = get_progress_service()
+    
+    async def run_nfo_scan():
+        """Run NFO scan phase with progress updates."""
+        try:
+            await perform_nfo_scan_phase(progress_service)
+            logger.info("NFO scan phase completed via API trigger")
+        except Exception as e:
+            logger.error("NFO scan phase failed: %s", e, exc_info=True)
+            if progress_service:
+                await progress_service.fail_progress(
+                    progress_id="nfo_scan",
+                    error_message=f"NFO scan failed: {str(e)}",
+                    metadata={"step_id": "nfo_scan", "phase": "nfo"}
+                )
+    
+    # Start NFO scan in background
+    asyncio.create_task(run_nfo_scan())
+    
+    return NfoScanPhaseResponse(
+        status="started",
+        message="NFO scan phase started. Check progress via WebSocket."
     )