Fix Dockerfile and add model preloading for HF Spaces

Dockerfile

@@ -1,7 +1,7 @@
 # ---------- build frontend ----------
 FROM node:20-bookworm AS frontend-build
 WORKDIR /frontend
-COPY frontend/package.json frontend/package-lock.json* ./
+COPY frontend/package.json ./
 RUN npm install
 COPY frontend/ .
 RUN npm run build

backend/app/main.py

@@ -26,6 +26,17 @@ def get_classifier_instance():
         classifier = get_classifier()
     return classifier
 
+@app.on_event("startup")
+async def startup_event():
+    """Preload the classifier on startup to avoid first-request delay."""
+    print("Preloading classifier on startup...")
+    try:
+        get_classifier_instance()
+        print("✅ Classifier loaded and ready!")
+    except Exception as e:
+        print(f"⚠️  Warning: Could not preload classifier: {e}")
+        print("Classifier will be loaded on first request.")
+
 # ---- API ----
 @app.get("/api/health")
 def health():