Add k3s deployment: Dockerfiles, nginx config, CI pipeline

- Backend Dockerfile: multi-stage rust:1.87 → debian:bookworm-slim
- Frontend Dockerfile: multi-stage node:22-alpine → nginx:alpine
- Frontend nginx.conf: serve static + proxy /api/ to backend service
- Change API_URL to relative /api for containerized deployment
- Woodpecker CI pipeline to build and push images to Gitea Registry
- Add repository URL to CLAUDE.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/Dockerfile

@@ -0,0 +1,16 @@
+FROM node:22-alpine AS builder
+
+WORKDIR /app
+COPY package.json package-lock.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
+
+CMD ["nginx", "-g", "daemon off;"]