Task 8: Standardize modeling style (TypedDict vs Pydantic)

Convert inconsistent modeling style to standardized Pydantic models for all
external-facing data structures while maintaining TypedDict compatibility where
appropriate for internal layer-private structures.

Changes:
- Converted IpLookupResult TypedDict to use IpLookupResponse Pydantic model
  in jail_service.lookup_ip() for consistency with routers
- Added GeoCacheEntry Pydantic model for geo cache repository rows
- Converted GeoCacheRow TypedDict to use GeoCacheEntry alias
- Converted ImportLogRow TypedDict to use ImportLogEntry alias
- Updated routers and services to work with Pydantic models
- Updated all tests to use Pydantic model field access (attributes)
  instead of dict subscripting

Documentation:
- Added 'Model Type Usage by Layer' section to Backend-Development.md
- Defines when TypedDict is allowed (internal structures) vs Pydantic
  (external-facing, cross-boundary data)
- Provides clear guidance on modeling conventions per layer

Benefits:
- Consistent validation and serialization behavior
- Better IDE support and type checking
- Clearer separation of concerns by layer
- Reduced maintenance cost from mixed validation approaches

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/tests/test_services/test_jail_service.py

@@ -847,8 +847,8 @@ class TestLookupIp:
         with _patch_client(responses):
             result = await jail_service.lookup_ip(_SOCKET, "1.2.3.4")
 
-        assert result["ip"] == "1.2.3.4"
-        assert "sshd" in result["currently_banned_in"]
+        assert result.ip == "1.2.3.4"
+        assert "sshd" in result.currently_banned_in
 
     async def test_geo_enricher_returns_geo_detail(self) -> None:
         """lookup_ip converts GeoInfo from the enricher into GeoDetail."""
@@ -868,11 +868,11 @@ class TestLookupIp:
                 geo_enricher=_enricher,
             )
 
-        assert isinstance(result["geo"], GeoDetail)
-        assert result["geo"].country_code == "DE"
-        assert result["geo"].country_name == "Germany"
-        assert result["geo"].asn == "AS123"
-        assert result["geo"].org == "Acme"
+        assert isinstance(result.geo, GeoDetail)
+        assert result.geo.country_code == "DE"
+        assert result.geo.country_name == "Germany"
+        assert result.geo.asn == "AS123"
+        assert result.geo.org == "Acme"
 
     async def test_http_session_uses_geo_service_lookup(self) -> None:
         """lookup_ip uses geo_service.lookup when http_session is provided."""
@@ -896,11 +896,11 @@ class TestLookupIp:
             )
 
         mock_lookup.assert_awaited_once_with("1.2.3.4", mock_session)
-        assert isinstance(result["geo"], GeoDetail)
-        assert result["geo"].country_code == "JP"
-        assert result["geo"].country_name == "Japan"
-        assert result["geo"].asn is None
-        assert result["geo"].org is None
+        assert isinstance(result.geo, GeoDetail)
+        assert result.geo.country_code == "JP"
+        assert result.geo.country_name == "Japan"
+        assert result.geo.asn is None
+        assert result.geo.org is None
 
     async def test_invalid_ip_raises(self) -> None:
         """lookup_ip raises ValueError for invalid IP."""
@@ -917,7 +917,7 @@ class TestLookupIp:
         with _patch_client(responses):
             result = await jail_service.lookup_ip(_SOCKET, "9.9.9.9")
 
-        assert result["currently_banned_in"] == []
+        assert result.currently_banned_in == []
 
 
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