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_routers/test_geo.py

@@ -70,7 +70,7 @@ class TestGeoLookup:
     async def test_200_with_geo_info(self, geo_client: AsyncClient) -> None:
         """GET /api/geo/lookup/{ip} returns 200 with enriched result."""
         geo = GeoInfo(country_code="DE", country_name="Germany", asn="12345", org="Acme")
-        result = {
+        result: dict[str, object] = {
             "ip": "1.2.3.4",
             "currently_banned_in": ["sshd"],
             "geo": geo,
@@ -92,7 +92,7 @@ class TestGeoLookup:
 
     async def test_200_when_not_banned(self, geo_client: AsyncClient) -> None:
         """GET /api/geo/lookup/{ip} returns empty list when IP is not banned anywhere."""
-        result = {
+        result: dict[str, object] = {
             "ip": "8.8.8.8",
             "currently_banned_in": [],
             "geo": GeoInfo(country_code="US", country_name="United States", asn=None, org=None),
@@ -108,7 +108,7 @@ class TestGeoLookup:
 
     async def test_200_with_no_geo(self, geo_client: AsyncClient) -> None:
         """GET /api/geo/lookup/{ip} returns null geo when enricher fails."""
-        result = {
+        result: dict[str, object] = {
             "ip": "1.2.3.4",
             "currently_banned_in": [],
             "geo": None,
@@ -144,7 +144,7 @@ class TestGeoLookup:
 
     async def test_ipv6_address(self, geo_client: AsyncClient) -> None:
         """GET /api/geo/lookup/{ip} handles IPv6 addresses."""
-        result = {
+        result: dict[str, object] = {
             "ip": "2001:db8::1",
             "currently_banned_in": [],
             "geo": None,