feat(docker): add Docker Compose deployment for Dokploy

- backend/Dockerfile: Python 3.12-slim, uvicorn on port 8000
- frontend/Dockerfile: multi-stage Node build + nginx:alpine serve
- frontend/nginx.conf: proxy /api to backend, SPA routing for Vue Router
- docker-compose.yml: backend+frontend services with Traefik labels
- fix(cors): use settings.frontend_url instead of hardcoded localhost

Fixes Nixpacks detection failure (requirements.txt/package.json not at root).

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

frontend/Dockerfile

@@ -0,0 +1,13 @@
+FROM node:20-alpine AS builder
+
+WORKDIR /app
+COPY package*.json ./
+RUN npm ci
+COPY . .
+RUN npm run build
+
+FROM nginx:alpine
+COPY --from=builder /app/dist /usr/share/nginx/html
+COPY nginx.conf /etc/nginx/conf.d/default.conf
+
+EXPOSE 80