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_repositories/test_geo_cache_repo.py

@@ -82,7 +82,7 @@ async def test_load_all_and_count_unresolved(tmp_path: Path) -> None:
         unresolved = await geo_cache_repo.count_unresolved(db)
 
     assert unresolved == 1
-    assert any(row["ip"] == "6.6.6.6" and row["country_code"] == "FR" for row in rows)
+    assert any(row.ip == "6.6.6.6" and row.country_code == "FR" for row in rows)
 
 
 @pytest.mark.asyncio