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/dtos/post.py

@@ -1,4 +1,9 @@
-"""DTOs for post use cases."""
+"""DTOs for post use cases.
+
+This module defines Data Transfer Objects used for communication between
+application layer use cases and presentation layer. DTOs are immutable
+dataclasses that carry data across process boundaries.
+"""
 
 from dataclasses import dataclass
 from datetime import datetime
@@ -7,7 +12,25 @@ from uuid import UUID
 
 @dataclass(frozen=True)
 class CreatePostDTO:
-    """DTO for creating a post."""
+    """DTO for creating a post.
+
+    Carries post creation data from API to use case.
+    Contains all required fields for post creation.
+
+    Attributes:
+        title: Post title string.
+        content: Post content string.
+        author_id: Identifier of the post author.
+        tags: Optional list of tags for categorization.
+
+    Example:
+        >>> dto = CreatePostDTO(
+        ...     title="My Post",
+        ...     content="Content here...",
+        ...     author_id="user-123",
+        ...     tags=["python"]
+        ... )
+    """
 
     title: str
     content: str
@@ -17,7 +40,19 @@ class CreatePostDTO:
 
 @dataclass(frozen=True)
 class UpdatePostDTO:
-    """DTO for updating a post."""
+    """DTO for updating a post.
+
+    Carries optional post update data. All fields are optional
+    allowing partial updates.
+
+    Attributes:
+        title: Optional new title.
+        content: Optional new content.
+        tags: Optional new tags list.
+
+    Example:
+        >>> dto = UpdatePostDTO(title="Updated Title")
+    """
 
     title: str | None = None
     content: str | None = None
@@ -26,7 +61,35 @@ class UpdatePostDTO:
 
 @dataclass(frozen=True)
 class PostResponseDTO:
-    """DTO for post response."""
+    """DTO for post response.
+
+    Carries complete post data for API responses.
+    Includes all post attributes and metadata.
+
+    Attributes:
+        id: Unique post identifier.
+        title: Post title.
+        content: Post content.
+        slug: URL-friendly slug.
+        author_id: Author identifier.
+        published: Publication status.
+        tags: List of tags.
+        created_at: Creation timestamp.
+        updated_at: Last update timestamp.
+
+    Example:
+        >>> dto = PostResponseDTO(
+        ...     id=uuid,
+        ...     title="Post",
+        ...     content="...",
+        ...     slug="post",
+        ...     author_id="user-123",
+        ...     published=True,
+        ...     tags=[],
+        ...     created_at=datetime.now(),
+        ...     updated_at=datetime.now()
+        ... )
+    """
 
     id: UUID
     title: str