Scaffold FastAPI + MySQL + Keycloak service with devcontainer

Sets up the project skeleton:

- FastAPI app factory with lifespan, request-id middleware, and RFC 9457
  problem+json error handlers
- Async SQLAlchemy 2.0 over MySQL (asyncmy), with a constraint naming
  convention in place before the first migration and async Alembic
- Keycloak as a pure resource server: OIDC discovery, cached JWKS with
  rotation-aware refresh, and require_roles dependencies
- Devcontainer running MySQL 8.4 and Keycloak 26.7 as compose siblings,
  with the realm (clients, roles, test users) imported on first boot
- Test suite covering the endpoints plus the token validator itself,
  exercised against a locally generated RSA keypair
- uv packaging, ruff, mypy --strict, pre-commit, Gitea CI, prod Dockerfile

Two Keycloak-in-containers traps are handled explicitly and documented in
the README: the issuer/internal-URL split (the browser sees localhost:8080,
the API sees keycloak:8080) and the audience mapper that stops Keycloak
issuing tokens with aud=account.

The devices resource is a placeholder proving the routing -> auth -> ORM ->
migration path end to end; replace it with the real domain.

Co-Authored-By: Claude Opus 5 <[email protected]>

.env.example

@@ -0,0 +1,25 @@
+# Copy to .env only if you need to override the devcontainer defaults.
+# The devcontainer supplies all of these through compose, so a fresh clone runs
+# with no .env file at all.
+
+APP_ENV=local
+DEBUG=true
+LOG_LEVEL=INFO
+
+# --- database ---------------------------------------------------------------
+DATABASE_URL=mysql+asyncmy://v2x:v2xpassword@mysql:3306/v2x?charset=utf8mb4
+TEST_DATABASE_URL=mysql+asyncmy://v2x:v2xpassword@mysql:3306/v2x_test?charset=utf8mb4
+
+# --- keycloak ---------------------------------------------------------------
+# These two URLs differ on purpose in local development; see README, "The two
+# URL traps". KEYCLOAK_ISSUER is compared against the token's `iss` claim and
+# must match the URL the *client* used. KEYCLOAK_INTERNAL_URL is how this
+# process reaches Keycloak on the container network.
+KEYCLOAK_ISSUER=http://localhost:8080/realms/v2x
+KEYCLOAK_INTERNAL_URL=http://keycloak:8080
+KEYCLOAK_REALM=v2x
+KEYCLOAK_AUDIENCE=v2x-api
+KEYCLOAK_SWAGGER_CLIENT_ID=v2x-swagger
+
+# --- http -------------------------------------------------------------------
+CORS_ORIGINS=["http://localhost:3000","http://localhost:8000"]