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/domain/exceptions.py

@@ -1,39 +1,78 @@
-"""Domain exceptions."""
+"""Domain exceptions for business logic errors.
+
+This module defines the exception hierarchy for domain layer errors.
+All domain exceptions inherit from DomainException base class.
+"""
 
 
 class DomainException(Exception):
-    """Base exception for domain layer."""
+    """Base exception for domain layer.
+
+    All domain-specific exceptions should inherit from this class.
+    Provides a consistent interface for error messages.
+
+    Attributes:
+        message: Human-readable error description.
+
+    Example:
+        >>> raise DomainException("Business rule violated")
+    """
 
     def __init__(self, message: str) -> None:
+        """Initialize domain exception.
+
+        Args:
+            message: Error message describing the exception.
+        """
         self.message = message
         super().__init__(self.message)
 
 
 class ValidationException(DomainException):
-    """Raised when validation fails."""
+    """Raised when validation fails.
 
-    pass
+    Used when entity or value object validation does not pass.
+
+    Example:
+        >>> raise ValidationException("Title is too long")
+    """
 
 
 class NotFoundException(DomainException):
-    """Raised when an entity is not found."""
+    """Raised when an entity is not found.
 
-    pass
+    Used when requesting an entity that does not exist in the repository.
+
+    Example:
+        >>> raise NotFoundException("Post with id 123 not found")
+    """
 
 
 class AlreadyExistsException(DomainException):
-    """Raised when trying to create an entity that already exists."""
+    """Raised when trying to create an entity that already exists.
 
-    pass
+    Used when attempting to create a duplicate entity.
+
+    Example:
+        >>> raise AlreadyExistsException("Post with this slug already exists")
+    """
 
 
 class UnauthorizedException(DomainException):
-    """Raised when user is not authorized."""
+    """Raised when user is not authorized.
 
-    pass
+    Used when authentication is required but not provided or invalid.
+
+    Example:
+        >>> raise UnauthorizedException("Authentication required")
+    """
 
 
 class ForbiddenException(DomainException):
-    """Raised when access is forbidden."""
+    """Raised when access is forbidden.
 
-    pass
+    Used when authenticated user lacks required permissions.
+
+    Example:
+        >>> raise ForbiddenException("Only admins can delete posts")
+    """