Add news feature with CRUD operations and real-time notifications

- Implemented news management functionality, allowing admins to create, read, update, and delete news posts.
- Introduced a new SignalR event for broadcasting news updates to all connected clients.
- Updated API documentation to include new endpoints for news management.
- Enhanced frontend with a dedicated news page and admin interface for managing news posts.
- Added necessary localization for news-related terms in both Russian and English.

docs/backend-conventions.md

@@ -12,6 +12,7 @@ backend/
       Common/            # Entity (единственный базовый класс — без AggregateRoot/IDomainEvent)
       Activation/         # ActivationRequest, ActivationStatus
       Apps/               # ClientApp, OsPlatform
+      News/                # NewsPost
       Audit/              # AuditLog, AuditSource
       Configs/            # VpnConfig, ConfigStatus, TrafficSample
       Inbounds/           # Inbound, VpnProtocol
@@ -29,6 +30,7 @@ backend/
       Admin/
         Activation/       # ListActivationRequestsQuery, Approve/RejectActivationCommand
         Apps/             # CRUD ClientApp
+        News/              # CRUD NewsPost
         Audit/            # ListAuditLogsQuery
         Inbounds/         # ListInbounds, PublishInbound
         Nodes/            # RegisterNode, UpdateNode, DeleteNode, SyncNode, ProbeNode, ListNodes
@@ -37,6 +39,7 @@ backend/
         Users/            # ListUsers, BlockUser/UnblockUser, ChangeUserRole, ResetUserPassword,
                           # ForceRevokeConfig, GetUserConfigs
       Apps/               # ListAppsQuery (по ОС, для юзера)
+      News/               # ListNewsQuery (пагинировано, для юзера)
       Auth/
         ChangePassword/, DeleteMyAccount/, Login/, Logout/, Me/, Refresh/, Register/
       Configs/
@@ -59,7 +62,7 @@ backend/
       Telegram/          # TelegramNotifier, TelegramOptions
       DependencyInjection.cs   # AddInfrastructure(...)
     PnvPanel.Api/
-      Endpoints/         # 12 файлов, см. backend-conventions.md ниже и api-design.md
+      Endpoints/         # 14 файлов, см. backend-conventions.md ниже и api-design.md
       Hubs/              # PanelHub, SignalRRealtimeNotifier (реализация IRealtimeNotifier — здесь,
                           # не в Infrastructure, т.к. нужен IHubContext<PanelHub>)
       Telegram/          # TelegramBotHostedService, PnvBotUpdateHandler, TelegramNotifier