refactor: improve backend type safety and import organization

- Add TYPE_CHECKING guards for runtime-expensive imports (aiohttp, aiosqlite)
- Reorganize imports to follow PEP 8 conventions
- Convert TypeAlias to modern PEP 695 type syntax (where appropriate)
- Use Sequence/Mapping from collections.abc for type hints (covariant)
- Replace string literals with cast() for improved type inference
- Fix casting of Fail2BanResponse and TypedDict patterns
- Add IpLookupResult TypedDict for precise return type annotation
- Reformat overlong lines for readability (120 char limit)
- Add asyncio_mode and filterwarnings to pytest config
- Update test fixtures with improved type hints

This improves mypy type checking and makes type relationships explicit.

backend/tests/test_services/test_history_service.py

@@ -64,7 +64,7 @@ async def _create_f2b_db(path: str, rows: list[dict[str, Any]]) -> None:
 
 
 @pytest.fixture
-async def f2b_db_path(tmp_path: Path) -> str:  # type: ignore[misc]
+async def f2b_db_path(tmp_path: Path) -> str:
     """Return the path to a test fail2ban SQLite database."""
     path = str(tmp_path / "fail2ban_test.sqlite3")
     await _create_f2b_db(