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]>

docker/mysql/init/01-databases.sql

@@ -0,0 +1,13 @@
+-- Runs once, on the first boot of an empty mysql-data volume.
+--
+-- MYSQL_DATABASE/MYSQL_USER in compose.yaml already create `v2x` and grant the
+-- app user on it. This adds the separate database the test suite runs against,
+-- so tests never touch development data.
+
+CREATE DATABASE IF NOT EXISTS v2x_test
+  CHARACTER SET utf8mb4
+  COLLATE utf8mb4_0900_ai_ci;
+
+GRANT ALL PRIVILEGES ON v2x_test.* TO 'v2x'@'%';
+
+FLUSH PRIVILEGES;