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/app/repositories/geo_cache_repo.py

@@ -9,22 +9,18 @@ connection lifetimes.
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, TypedDict
+from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
     from collections.abc import Sequence
 
     import aiosqlite
 
+from app.models.geo import GeoCacheEntry
 
-class GeoCacheRow(TypedDict):
-    """A single row from the ``geo_cache`` table."""
 
-    ip: str
-    country_code: str | None
-    country_name: str | None
-    asn: str | None
-    org: str | None
+# Alias for backward compatibility with protocols
+GeoCacheRow = GeoCacheEntry
 
 
 async def load_all(db: aiosqlite.Connection) -> list[GeoCacheRow]: