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/routers/geo.py

@@ -13,12 +13,15 @@ from typing import TYPE_CHECKING, Annotated
 if TYPE_CHECKING:
     import aiohttp
 
+    from app.services.jail_service import IpLookupResult
+
 import aiosqlite
 from fastapi import APIRouter, Depends, HTTPException, Path, Request, status
 
 from app.dependencies import AuthDep, get_db
 from app.models.geo import GeoCacheStatsResponse, GeoDetail, IpLookupResponse
 from app.services import geo_service, jail_service
+from app.services.geo_service import GeoInfo
 from app.utils.fail2ban_client import Fail2BanConnectionError
 
 router: APIRouter = APIRouter(prefix="/api/geo", tags=["Geo"])
@@ -61,7 +64,7 @@ async def lookup_ip(
         return await geo_service.lookup(addr, http_session)
 
     try:
-        result = await jail_service.lookup_ip(
+        result: IpLookupResult = await jail_service.lookup_ip(
             socket_path,
             ip,
             geo_enricher=_enricher,
@@ -77,9 +80,9 @@ async def lookup_ip(
             detail=f"Cannot reach fail2ban: {exc}",
         ) from exc
 
-    raw_geo = result.get("geo")
+    raw_geo = result["geo"]
     geo_detail: GeoDetail | None = None
-    if raw_geo is not None:
+    if isinstance(raw_geo, GeoInfo):
         geo_detail = GeoDetail(
             country_code=raw_geo.country_code,
             country_name=raw_geo.country_name,