docs: add AI code generation requirements and comprehensive Google-style docstrings

- Add AI code generation requirements to AGENTS.md
- Add module-level docstrings to all 46 Python modules
- Add detailed Google-style docstrings to all classes and functions
- Remove all inline comments following self-documenting code principle
- Include Args, Returns, Raises sections in function docstrings
- Add Attributes and Examples sections to class docstrings

app/infrastructure/__init__.py

@@ -1,4 +1,8 @@
-"""Infrastructure layer exports."""
+"""Infrastructure layer exports.
+
+This module re-exports all infrastructure components including
+config, database, repositories, DI, and middleware.
+"""
 
 from app.infrastructure.config import Settings, settings
 from app.infrastructure.database import (
@@ -15,10 +19,8 @@ from app.infrastructure.middleware import register_exception_handlers
 from app.infrastructure.repositories import SQLAlchemyPostRepository
 
 __all__ = [
-    # Config
     "Settings",
     "settings",
-    # Database
     "Base",
     "PostORM",
     "engine",
@@ -26,10 +28,7 @@ __all__ = [
     "get_session",
     "init_db",
     "close_db",
-    # Repositories
     "SQLAlchemyPostRepository",
-    # DI
     "create_container",
-    # Middleware
     "register_exception_handlers",
 ]