fix: correct import path and type issues in db migration deduplication

- Fix import to use correct app_config from basic_memory.config
- Remove unused imports in test file
- Resolve type checker errors for app_config parameter

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: phernandez

src/basic_memory/db.py

@@ -99,8 +99,8 @@ async def get_or_create_db(
         # Run migrations automatically unless explicitly disabled
         if ensure_migrations:
             if app_config is None:
-                from basic_memory.config import get_basic_memory_config
-                app_config = get_basic_memory_config()
+                from basic_memory.config import app_config as global_app_config
+                app_config = global_app_config
             await run_migrations(app_config, db_type)
 
     # These checks should never fail since we just created the engine and session maker

tests/test_db_migration_deduplication.py

@@ -1,10 +1,8 @@
 """Tests for database migration deduplication functionality."""
 
 import pytest
-from pathlib import Path
-from unittest.mock import patch, AsyncMock, call, MagicMock
+from unittest.mock import patch, AsyncMock, MagicMock
 
-from basic_memory.config import BasicMemoryConfig
 from basic_memory import db