Add instructions management functionality and update related components

- Introduced new endpoints for managing instruction intros and tabs, allowing admins to create, update, and delete instructional content.
- Enhanced the FactoryResetCommandHandler to include the seeding of instruction data during a factory reset.
- Updated the database schema to include InstructionIntro and InstructionTab entities, with corresponding migrations.
- Improved frontend routing and components to support the new instructions section, including a dedicated page for displaying instructions and tabs.
- Enhanced API documentation to reflect the new instruction management features and their expected request/response formats.
- Added localization support for the new instructions functionality in both Russian and English.

backend/src/PnvPanel.Application/Common/Interfaces/IAppDbContext.cs

@@ -5,6 +5,7 @@ using PnvPanel.Domain.Apps;
 using PnvPanel.Domain.Audit;
 using PnvPanel.Domain.Configs;
 using PnvPanel.Domain.Inbounds;
+using PnvPanel.Domain.Instructions;
 using PnvPanel.Domain.News;
 using PnvPanel.Domain.Nodes;
 using PnvPanel.Domain.Support;
@@ -40,6 +41,10 @@ public interface IAppDbContext
 
     DbSet<TicketAttachment> TicketAttachments { get; }
 
+    DbSet<InstructionIntro> InstructionIntros { get; }
+
+    DbSet<InstructionTab> InstructionTabs { get; }
+
     /// <summary>Нужен для advisory-lock при проверке квоты конфигов (см. CreateVpnConfigCommandHandler).</summary>
     DatabaseFacade Database { get; }
 

backend/src/PnvPanel.Application/Common/Interfaces/IInstructionIntroSeeder.cs

@@ -0,0 +1,10 @@
+namespace PnvPanel.Application.Common.Interfaces;
+
+/// <summary>
+/// Сидинг дефолтного вводного текста страницы инструкций. Идемпотентно — не трогает таблицу, если
+/// в ней уже есть строка (используется и при старте, и после полного сброса панели).
+/// </summary>
+public interface IInstructionIntroSeeder
+{
+    Task SeedIfEmptyAsync(CancellationToken cancellationToken);
+}