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/interfaces/transaction_manager.py

@@ -1,17 +1,38 @@
-"""Transaction Manager interface for managing database transactions."""
+"""Transaction Manager interface for managing database transactions.
+
+This module defines the abstract interface for transaction management.
+Implementations control transaction boundaries for use cases.
+"""
 
 from abc import ABC, abstractmethod
 
 
 class TransactionManager(ABC):
-    """Abstract Transaction Manager for controlling transaction boundaries."""
+    """Abstract Transaction Manager for controlling transaction boundaries.
+
+    Provides interface for committing or rolling back database transactions.
+    Used by use cases to manage atomic operations.
+
+    Example:
+        >>> async with transaction_manager:
+        ...     await repository.add(entity)
+        ...     await transaction_manager.commit()
+    """
 
     @abstractmethod
     async def commit(self) -> None:
-        """Commit the current transaction."""
+        """Commit the current transaction.
+
+        Persists all pending changes to the database.
+        Should be called after all operations succeed.
+        """
         ...
 
     @abstractmethod
     async def rollback(self) -> None:
-        """Rollback the current transaction."""
+        """Rollback the current transaction.
+
+        Discards all pending changes.
+        Should be called when an error occurs.
+        """
         ...