Add Docker support

- Dockerfile: multi-stage Python 3.12 slim build
- docker-compose.yml: app + PostgreSQL 16 with healthcheck
- requirements.txt: fastapi, uvicorn, psycopg, passlib, jose
- .dockerignore: exclude venv, pycache, secrets
- app.py: env-based DB config (DB_HOST/PORT/NAME/USER/PASSWORD)
- README: Docker deploy instructions

.dockerignore

@@ -0,0 +1,9 @@
+.venv/
+__pycache__/
+*.pyc
+.env
+.git
+.gitignore
+*.log
+.dbpass
+migrations/_migrations*