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/application/__init__.py

@@ -1,4 +1,8 @@
-"""Application layer exports."""
+"""Application layer exports.
+
+This module re-exports all application layer components including
+DTOs, interfaces, and use cases for convenient importing.
+"""
 
 from app.application.dtos import CreatePostDTO, PostResponseDTO, UpdatePostDTO
 from app.application.interfaces import TransactionManager
@@ -12,13 +16,10 @@ from app.application.use_cases import (
 )
 
 __all__ = [
-    # DTOs
     "CreatePostDTO",
     "UpdatePostDTO",
     "PostResponseDTO",
-    # Interfaces
     "TransactionManager",
-    # Use Cases
     "CreatePostUseCase",
     "GetPostUseCase",
     "UpdatePostUseCase",