feat: implement NPM Proxy Hosts section with reusable entity patterns

Add full Proxy Hosts feature for Control Room:
- Data layer: datasource, model with custom JSON converters for NPM API quirks
- Domain layer: ProxyHost entity with SSL, caching, websocket support
- Presentation: list page, detail/edit page, form widget

Add reusable entity page patterns for Control Room sections:
- EntityPageScaffold, EntitySection, EntitySettingRow components
- EntityForm with create/view/edit mode support
- EntityPageModeMixin for consistent mode management
- CreateOnlyField for immutable-after-creation fields

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/features/control_room/presentation/pages/control_room_page.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart' hide Stack;
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:go_router/go_router.dart';
 import 'package:tatlock_ui/features/control_room/containers/presentation/pages/containers_list_page.dart';
+import 'package:tatlock_ui/features/control_room/npm/presentation/pages/proxy_hosts_page.dart';
 import 'package:tatlock_ui/features/control_room/router.dart';
 import 'package:tatlock_ui/features/control_room/stacks/data/repositories/stack_repository_impl.dart';
 import 'package:tatlock_ui/features/control_room/stacks/domain/entities/stack.dart';
@@ -71,6 +72,8 @@ class _SectionContent extends ConsumerWidget {
     switch (nav) {
       case ControlRoomNav.containers:
         return const _ContainersSection();
+      case ControlRoomNav.proxyHosts:
+        return const ProxyHostsPage();
       default:
         return _PlaceholderSection(nav: nav);
     }