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/services/history_service.py

@@ -11,10 +11,12 @@ modifies or locks the fail2ban database.
 from __future__ import annotations
 
 from datetime import UTC, datetime
+from typing import TYPE_CHECKING
 
 import structlog
 
-from app.services.geo_service import GeoEnricher
+if TYPE_CHECKING:
+    from app.services.geo_service import GeoEnricher
 
 from app.models.ban import TIME_RANGE_SECONDS, TimeRange
 from app.models.history import (