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

AGENTS.md

@@ -110,6 +110,82 @@ tests/
 - Use **Repository** pattern for data access
 - Use **Dependency Injection** via FastAPI's Depends()
 
+## AI Code Generation Requirements
+
+### Documentation Standards
+- **Write self-documenting code** - use clear, descriptive variable names and function names
+- **NO inline comments** - code should be readable without explanatory comments
+- **Google-style docstrings** are REQUIRED for all modules, classes, and functions
+
+### Docstring Requirements
+
+#### Modules
+Every module must have a module-level docstring:
+```python
+"""Module for managing blog posts.
+
+This module provides use cases for creating, updating, and deleting
+blog posts in the application layer.
+"""
+```
+
+#### Classes
+Every class must have a detailed docstring:
+```python
+class CreatePostUseCase:
+    """Use case for creating a new blog post.
+
+    This class encapsulates the business logic for creating posts,
+    including validation and slug generation.
+
+    Attributes:
+        uow: Unit of Work for database transactions.
+        slug_service: Service for generating URL-friendly slugs.
+
+    Example:
+        >>> use_case = CreatePostUseCase(uow, slug_service)
+        >>> result = await use_case.execute(dto)
+    """
+```
+
+#### Functions/Methods
+Every function must have a detailed docstring with Args, Returns, Raises:
+```python
+async def execute(self, dto: CreatePostDTO) -> PostDTO:
+    """Execute the use case to create a new post.
+
+    Args:
+        dto: Data transfer object containing post creation data
+            including title, content, and author information.
+
+    Returns:
+        PostDTO: The created post data transfer object with
+            generated ID and slug.
+
+    Raises:
+        TitleValidationError: If the title is empty or too long.
+        ContentValidationError: If the content is empty.
+        DuplicateSlugError: If a post with the same slug exists.
+
+    Note:
+        This method is idempotent - calling it multiple times with
+        the same data will create separate posts with unique slugs.
+    """
+```
+
+### Google-Style Docstring Format
+
+Use the following sections as appropriate:
+- `Args` - Parameter descriptions with types
+- `Returns` - Return value description with type
+- `Raises` - Exceptions that may be raised
+- `Yields` - For generator functions
+- `Example` - Usage examples
+- `Note` - Additional important information
+- `Warning` - Critical warnings
+- `Attributes` - For class attributes
+- `See Also` - References to related code
+
 ## DDD Concepts Used
 
 ### Entities