Standardize API response envelope shapes across all endpoints

This commit standardizes how API responses are wrapped, solving issue #24.

Problem:
- Inconsistent response envelopes (jails vs items vs bans vs no wrapper)
- Frontend required multiple field name variants
- Integration bugs from branching logic
- No clear pattern for different response types

Solution:
- Created response.py with base classes: PaginatedListResponse,
  CollectionResponse, CommandResponse
- Standardized all list/collection responses to use 'items' field
- Domain-specific field names for detail and aggregation responses
- Updated all backends routers and mappers
- Updated frontend types and hooks to match

Changes:
Backend:
- backend/app/models/response.py (new): Base response models
- backend/app/models/ban.py: Updated responses to inherit from bases
- backend/app/models/jail.py: Updated JailListResponse, JailCommandResponse
- backend/app/models/config.py: Updated collection responses
- backend/app/services/jail_service.py: Updated return statements
- backend/app/mappers/ban_mappers.py: Updated 'bans' to 'items'
- backend/tests/test_mappers/test_ban_mappers.py: Updated tests

Frontend:
- frontend/src/types/jail.ts: Updated response interfaces
- frontend/src/types/config.ts: Updated response interfaces
- frontend/src/hooks/useActiveBans.ts: Updated selector
- frontend/src/hooks/useJailList.ts: Updated selector
- frontend/src/hooks/useJailConfigs.ts: Updated selector
- frontend/src/hooks/useConfigActiveStatus.ts: Updated field access
- frontend/src/hooks/useJailAdmin.ts: Updated field access

Documentation:
- Docs/Backend-Development.md: Added § 4.1 API Response Envelope Policy

The policy defines:
1. Paginated lists use PaginatedListResponse (items, total, page, page_size)
2. Non-paginated collections use CollectionResponse (items, total)
3. Detail responses use entity-specific field names (jail, status, settings)
4. Command responses use CommandResponse (message, success, optional target)
5. Aggregations use domain-specific fields (jails, countries, buckets, bans)

All responses now follow one of these patterns, reducing frontend complexity.

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

backend/tests/test_mappers/test_ban_mappers.py

@@ -76,9 +76,9 @@ class TestActiveBanListMapper:
         result = map_domain_active_ban_list_to_response(domain_list)
 
         assert result.total == 2
-        assert len(result.bans) == 2
-        assert result.bans[0].ip == "1.1.1.1"
-        assert result.bans[1].ip == "2.2.2.2"
+        assert len(result.items) == 2
+        assert result.items[0].ip == "1.1.1.1"
+        assert result.items[1].ip == "2.2.2.2"
 
     def test_handles_empty_list(self) -> None:
         """Empty list is handled correctly."""
@@ -87,7 +87,7 @@ class TestActiveBanListMapper:
         result = map_domain_active_ban_list_to_response(domain_list)
 
         assert result.total == 0
-        assert len(result.bans) == 0
+        assert len(result.items) == 0
 
 
 class TestDashboardBanItemMapper: