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/app/repositories/import_log_repo.py

@@ -8,10 +8,11 @@ table.  All methods are plain async functions that accept a
 from __future__ import annotations
 
 import math
-from collections.abc import Mapping
 from typing import TYPE_CHECKING, TypedDict, cast
 
 if TYPE_CHECKING:
+    from collections.abc import Mapping
+
     import aiosqlite
 
 
@@ -165,5 +166,5 @@ def _row_to_dict(row: object) -> ImportLogRow:
     Returns:
         Dict mapping column names to Python values.
     """
-    mapping = cast(Mapping[str, object], row)
-    return cast(ImportLogRow, dict(mapping))
+    mapping = cast("Mapping[str, object]", row)
+    return cast("ImportLogRow", dict(mapping))