feat: Docker images, compose stacks, nginx config, Gitea CI

- site image: multi-stage node build -> unprivileged nginx (non-root, read-only)
- nginx: CSP + security headers, immutable asset caching, revalidated HTML,
  canonical trailing slash, preserved /Linkedin 301, legacy-WP 410s, custom 404
- externalise theme-init so CSP uses script-src 'self' (no inline hash)
- prod + dev compose; .env.example; relay Dockerfile fixed (image ships app user)
- Gitea Actions: quality, e2e, lighthouse budgets, relay build, image push on main
- verified: both images build; relay healthz 200; site serves EN/NO with CSP + redirect

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

deploy/docker-compose.yml

@@ -0,0 +1,47 @@
+# Production stack (DOCKER_SPEC §2). Publishes no host ports — the existing host
+# reverse proxy routes cesnimda.co.uk -> site:8080 and /api/contact -> relay:8081
+# over the shared external proxy network.
+
+services:
+  site:
+    build:
+      context: ../site
+      dockerfile: Dockerfile
+    image: git.cesnimda.uk/cesnimda/resumesite-site:latest
+    restart: unless-stopped
+    read_only: true
+    tmpfs:
+      - /tmp
+      - /var/cache/nginx
+      - /var/run
+    networks: [web]
+    logging:
+      driver: json-file
+      options: { max-size: '10m', max-file: '3' }
+
+  relay:
+    build:
+      context: ../relay
+      dockerfile: Dockerfile
+    image: git.cesnimda.uk/cesnimda/resumesite-relay:latest
+    restart: unless-stopped
+    read_only: true
+    environment:
+      - Smtp__Host=${SMTP_HOST}
+      - Smtp__Port=${SMTP_PORT:-587}
+      - Smtp__User=${SMTP_USER}
+      - Smtp__Password=${SMTP_PASSWORD}
+      - Relay__FromAddress=${RELAY_FROM:-}
+      - Relay__ToAddress=${RELAY_TO}
+      - Relay__AllowedOrigin=${RELAY_ALLOWED_ORIGIN:-https://cesnimda.co.uk}
+      - Relay__RateLimitPerWindow=${RELAY_RATE_LIMIT:-5}
+      - Relay__WindowSeconds=${RELAY_WINDOW_SECONDS:-600}
+    networks: [web]
+    logging:
+      driver: json-file
+      options: { max-size: '10m', max-file: '3' }
+
+networks:
+  web:
+    external: true
+    name: ${PROXY_NETWORK:-web}