Add OAuth2/OIDC per-user Gitea authentication

Introduce a GiteaOAuthValidator for JWT and userinfo validation and
fallbacks, add /oauth/token proxy, and thread per-user tokens through
the
request context and automation paths. Update config and .env.example for
OAuth-first mode, add OpenAPI, extensive unit/integration tests,
GitHub/Gitea CI workflows, docs, and lint/test enforcement (>=80% cov).

Makefile

@@ -35,10 +35,12 @@ install-dev:
 	pre-commit install
 
 test:
-	pytest tests/ -v --cov=aegis_gitea_mcp --cov-report=html --cov-report=term
+	pytest tests/ -v --cov=aegis_gitea_mcp --cov-report=html --cov-report=term --cov-fail-under=80
 
 lint:
 	ruff check src/ tests/
+	ruff format --check src/ tests/
+	black --check src/ tests/
 	mypy src/
 
 format: