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/routers/geo.py

@@ -8,10 +8,7 @@ Provides the IP enrichment endpoints:
 
 from __future__ import annotations
 
-from typing import TYPE_CHECKING, Annotated
-
-if TYPE_CHECKING:
-    from app.services.jail_service import IpLookupResult
+from typing import Annotated
 
 from fastapi import APIRouter, Path
 
@@ -57,14 +54,12 @@ async def lookup_ip(
         HTTPException: 400 when *ip* is not a valid IP address.
         HTTPException: 502 when fail2ban is unreachable.
     """
-    result: IpLookupResult = await jail_service.lookup_ip(
+    return await jail_service.lookup_ip(
         socket_path,
         ip,
         http_session=http_session,
     )
 
-    return IpLookupResponse(**result)
-
 
 # ---------------------------------------------------------------------------
 # POST /api/geo/re-resolve