feat(Dockerfile): add root multi-stage Dockerfile for Dokploy

- Stage 1 (node:20): builds Vue.js frontend to /app/dist
- Stage 2 (python:3.12): FastAPI serves API + static files
- main.py: serve Vue.js dist via StaticFiles if /app/dist exists
- Removes GET / route (replaced by frontend index.html)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,16 @@
+FROM node:20-alpine AS frontend-builder
+WORKDIR /app/frontend
+COPY frontend/package*.json ./
+RUN npm ci
+COPY frontend/ ./
+RUN npm run build
+
+FROM python:3.12-slim
+WORKDIR /app
+COPY backend/requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+COPY backend/ .
+COPY --from=frontend-builder /app/frontend/dist /app/dist
+RUN mkdir -p uploads
+EXPOSE 8000
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]