feat: add Docker deployment, web installer, and local test environment

- Multi-stage Dockerfiles for API (NestJS) and Web (Next.js standalone)
- docker-compose.prod.yml: full production stack (postgres, redis, keycloak,
  api, web) with optional Caddy/Let's Encrypt via --profile ssl
- docker-compose.local.yml: identical local test stack, all ports exposed
- docker/postgres/init.sql: auto-creates tos_app DB on first start
- Caddyfile: reverse proxy for app domain + auth subdomain
- install.sh: interactive installer (domain, SSL mode, secret generation)
- NestJS SetupModule: @Public() endpoints for /setup/status, /setup/admin,
  /setup/branding, /setup/complete with setup-token guard
- Web installer: 4-step flow (system check, admin creation, branding, complete)
  at /[locale]/setup/* with public middleware bypass
- i18n: installer namespace added to de.json and en.json
- CORS: x-setup-token header allowed in main.ts

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

docker/docker-compose.yml

@@ -27,6 +27,7 @@ services:
       - "${POSTGRES_PORT:-5432}:5432"
     volumes:
       - postgres_data:/var/lib/postgresql/data
+      - ./postgres/init.sql:/docker-entrypoint-initdb.d/init.sql:ro
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER:-tos_user} -d ${POSTGRES_DB:-tos_db}"]
       interval: 10s