Add Docker setup: one script to set up/start/stop the full stack

A new developer needs only Docker Desktop — no local Go, Node, or PostgreSQL.

- docker-compose.yml: PostgreSQL + Go API + Angular (nginx) with healthcheck,
  migrations auto-applied via docker-entrypoint-initdb.d, data in a volume
- backend/Dockerfile: static Go binary on distroless (nonroot)
- frontend/Dockerfile: Angular prod build served by nginx, which proxies /api
  to the api service (same origin, no CORS)
- docker.ps1: setup / start / stop / restart / reset / rebuild / status / logs;
  reads DB creds from backend/.env (single source, nothing duplicated)
- .dockerignore keeps .env and local artifacts out of image build contexts
- README: "Run with Docker" quick start

Not yet run end to end here (Docker is not installed on this machine); the
compose and script are validated for syntax and structure.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -0,0 +1,57 @@
+# TravelHub full stack on Docker. Drive it with docker.ps1 (which supplies the
+# DB_* values from backend/.env), or run docker compose directly after exporting
+# DB_USER / DB_PASSWORD / DB_NAME yourself.
+#
+#   PostgreSQL  internal only (data in the pgdata volume)
+#   api         Go API            -> http://localhost:8080
+#   web         Angular via nginx -> http://localhost:4200  (proxies /api to api)
+
+services:
+  postgres:
+    image: postgres:17
+    environment:
+      POSTGRES_USER: ${DB_USER:-postgres}
+      POSTGRES_PASSWORD: ${DB_PASSWORD:?set DB_PASSWORD (docker.ps1 reads it from backend/.env)}
+      POSTGRES_DB: ${DB_NAME:-travelhub}
+    volumes:
+      - pgdata:/var/lib/postgresql/data
+      # Migrations run once, on first creation of an empty data directory, in
+      # order (001_init, 002_seed, 003_demo_bookings). The seed generates
+      # flights relative to now(), so a fresh volume always has future-dated
+      # inventory. `docker.ps1 reset` wipes the volume to re-seed.
+      - ./backend/migrations:/docker-entrypoint-initdb.d:ro
+    healthcheck:
+      test: ['CMD-SHELL', 'pg_isready -U ${DB_USER:-postgres} -d ${DB_NAME:-travelhub}']
+      interval: 5s
+      timeout: 5s
+      retries: 12
+    restart: unless-stopped
+
+  api:
+    build: ./backend
+    environment:
+      DB_HOST: postgres
+      DB_PORT: '5432'
+      DB_USER: ${DB_USER:-postgres}
+      DB_PASSWORD: ${DB_PASSWORD}
+      DB_NAME: ${DB_NAME:-travelhub}
+      DB_SSLMODE: disable
+      PORT: '8080'
+      CORS_ORIGINS: http://localhost:4200
+    depends_on:
+      postgres:
+        condition: service_healthy
+    ports:
+      - '8080:8080'
+    restart: unless-stopped
+
+  web:
+    build: ./frontend
+    depends_on:
+      - api
+    ports:
+      - '4200:80'
+    restart: unless-stopped
+
+volumes:
+  pgdata: