feat: M1 foundation — compose stack, FastAPI, Google OAuth, encrypted tokens

- docker-compose with Postgres 16 + slim Python API image
- FastAPI app with session middleware, health endpoint, static login page
- Google OAuth (Authlib) with email invite-list whitelist; admin role support
- User + OAuthToken models; refresh tokens encrypted at rest (Fernet)
- Alembic migrations, run automatically on container startup
- Postgres backup/restore scripts for portability between machines

backend/requirements.txt

@@ -0,0 +1,11 @@
+fastapi>=0.115,<1.0
+uvicorn[standard]>=0.30,<1.0
+sqlalchemy>=2.0,<2.1
+psycopg[binary]>=3.2,<4.0
+alembic>=1.13,<2.0
+pydantic>=2.7,<3.0
+pydantic-settings>=2.3,<3.0
+authlib>=1.3,<2.0
+httpx>=0.27,<1.0
+itsdangerous>=2.1,<3.0
+cryptography>=42,<46