fix(gallery): add auth check to /api/image/sharpen endpoint (#2761)

Every other image-processing endpoint (denoise, upscale, remove-bg,
enhance-face, inpaint, harmonize) calls require_privilege(request,
"can_generate_images"). The sharpen endpoint was missing this check,
allowing unauthenticated users to trigger CPU-intensive image processing.

routes/gallery_routes.py

@@ -1316,6 +1316,7 @@ def setup_gallery_routes() -> APIRouter:
     @router.post("/api/image/sharpen")
     async def sharpen_image(request: Request):
         """Apply unsharp-mask sharpening to an image."""
+        require_privilege(request, "can_generate_images")
         body = await request.json()
         image_b64 = body.get("image")
         amount = body.get("amount", 50) / 100.0