docs, cli: enforce package-bound docs, add template scaffolding, and document CLI usage

- Restrict mkdocstrings generation to real Python packages (require __init__.py)
- Add explicit documentation section for CLI scaffolding and templates
- Generalize CLI to support multiple templates with dynamic discovery
- Package templates correctly for importlib.resources access
- Add fully documented health_app template (app entry point and handlers)
- Fix setuptools package-data configuration for bundled templates

These changes make documentation import-safe, clarify package boundaries,
and provide a deterministic, OpenAPI-first scaffolding workflow via CLI.

openapi_first/templates/health_app/main.py

@@ -1,3 +1,31 @@
+"""
+Application entry point for an OpenAPI-first FastAPI service.
+
+This module constructs a FastAPI application exclusively from an
+OpenAPI specification and a handler namespace, without using
+decorator-driven routing.
+
+All HTTP routes, methods, and operation bindings are defined in the
+OpenAPI document referenced by ``openapi_path``. Python callables
+defined in the ``routes`` module are bound to OpenAPI operations
+strictly via ``operationId``.
+
+This module contains no routing logic, request handling, or framework
+configuration beyond application assembly.
+
+Design guarantees:
+- OpenAPI is the single source of truth
+- No undocumented routes can exist
+- Every OpenAPI operationId must resolve to exactly one handler
+- All contract violations fail at application startup
+
+This file is intended to be used as the ASGI entry point.
+
+Example:
+    uvicorn main:app
+"""
+
+
 from openapi_first.app import OpenAPIFirstApp
 import routes