Add diagnostics endpoints and types for improved system monitoring

Implemented new diagnostics endpoints in the API and added corresponding route configurations in the frontend. Introduced types for diagnostics data, including host, forwarding, and system diagnostics, to enhance monitoring capabilities. Updated localization files to support diagnostics UI elements in both English and Russian, ensuring a comprehensive user experience.

frontend/src/features/admin/diagnostics/api.ts

@@ -0,0 +1,7 @@
+import { apiRequest } from '@/shared/api/client'
+import type { DiagnosticsDto } from '@/shared/api/types'
+
+/** Снимок диагностики: форвардинг, БД, хранилище, ffmpeg. Пересчитывается на каждый запрос. */
+export function getDiagnostics() {
+  return apiRequest<DiagnosticsDto>('/admin/diagnostics')
+}