add spec-driven auth dependency injection

- security.py: parse securitySchemes, resolve {ENV_VAR} from env,
  generate FastAPI Depends for Bearer JWT introspection
- app.py: extract schemes, build deps, pass to binder at init
- binder.py: inject Depends() per operation based on spec's security
- __init__.py: export security module
- pyproject.toml: add httpx dependency

pyproject.toml

@@ -55,6 +55,9 @@ dependencies = [
 
     # Code generation
     "datamodel-code-generator>=0.25.0",
+
+    # HTTP client for service-to-service (token introspection)
+    "httpx>=0.27.0",
 ]
 
 [project.scripts]