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/geo_cache_repo.py

@@ -12,6 +12,8 @@ from __future__ import annotations
 from typing import TYPE_CHECKING, TypedDict
 
 if TYPE_CHECKING:
+    from collections.abc import Sequence
+
     import aiosqlite
 
 
@@ -112,7 +114,7 @@ async def upsert_neg_entry(db: aiosqlite.Connection, ip: str) -> None:
 
 async def bulk_upsert_entries(
     db: aiosqlite.Connection,
-    rows: list[tuple[str, str | None, str | None, str | None, str | None]],
+    rows: Sequence[tuple[str, str | None, str | None, str | None, str | None]],
 ) -> int:
     """Bulk insert or update multiple geo cache entries."""
     if not rows: