Fix frontend production deployment and health check port

[BrandonS7]

What this does

1. Frontend Dockerfile - production build

The current Dockerfile runs npm run dev (Vite dev server) in production. This exposes source maps, hot module replacement, and dev tooling to the public internet.

Replaced with a proper multi-stage build:

• Build stage: npm ci + npm run build on Node 20 Alpine
• Runtime stage: Serves static dist/ via Nginx Alpine

Added frontend/nginx.conf with SPA routing (try_files fallback to index.html) and long-lived cache headers for static assets.

2. Health check port fix

The docker-compose.yml health check was probing localhost:8001 but the backend listens on port 8000. Fixed to match the actual application port.

3. Compose cleanup

• Updated frontend port mapping from 5174:5173 to 5174:8080 (Nginx)
• Removed dev hot-reload volume mount (not applicable with production build)

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Minimal changes, no backend modifications.