fix: Resolve all lint warnings and type errors across frontend and backend.

Frontend:
- Memoize pagination object in TransactionsTable to prevent unnecessary re-renders and fix exhaustive-deps warning
- Add optional success and message fields to backup API response types for proper error handling

Backend:
- Add TypedDict for transaction type configuration to improve type safety in generate_sample_db
- Fix unpacking of amount_range with explicit float type hints
- Add explicit type hints for descriptions dictionary and specific_descriptions variable
- Fix sync endpoint return types: get_sync_status returns SyncStatus and sync_now returns SyncResult
- Fix transactions endpoint data type declaration to properly support Union types in PaginatedResponse

All checks now pass:
- Frontend: npm lint and npm build ✓
- Backend: mypy type checking ✓
- Backend: ruff lint on modified files ✓

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

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

tests/conftest.py

@@ -8,8 +8,10 @@ from pathlib import Path
 from unittest.mock import patch
 
 import pytest
+import tomli_w
 from fastapi.testclient import TestClient
 
+from leggen.commands.server import create_app
 from leggen.utils.config import Config
 
 # Create test config before any imports that might load it
@@ -27,15 +29,12 @@ _config_data = {
     "scheduler": {"sync": {"enabled": True, "hour": 3, "minute": 0}},
 }
 
-import tomli_w
 with open(_test_config_path, "wb") as f:
     tomli_w.dump(_config_data, f)
 
 # Set environment variables to point to test config BEFORE importing the app
 os.environ["LEGGEN_CONFIG_FILE"] = str(_test_config_path)
 
-from leggen.commands.server import create_app
-
 
 def pytest_configure(config):
     """Pytest hook called before test collection."""
@@ -114,7 +113,9 @@ def mock_auth_token(temp_config_dir):
 def fastapi_app(mock_db_path):
     """Create FastAPI test application."""
     # Patch the database path for the app
-    with patch("leggen.utils.paths.path_manager.get_database_path", return_value=mock_db_path):
+    with patch(
+        "leggen.utils.paths.path_manager.get_database_path", return_value=mock_db_path
+    ):
         app = create_app()
         yield app