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/tests/PnvPanel.Application.Tests/Admin/Instructions/InstructionTabCommandHandlerTests.cs

@@ -0,0 +1,97 @@
+using PnvPanel.Application.Admin.Instructions;
+using PnvPanel.Application.Tests.TestSupport;
+using PnvPanel.Domain.Instructions;
+using Xunit;
+
+namespace PnvPanel.Application.Tests.Admin.Instructions;
+
+public class InstructionTabCommandHandlerTests
+{
+    [Fact]
+    public async Task Create_AddsTab()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var handler = new CreateInstructionTabCommandHandler(dbContext);
+
+        var result = await handler.Handle(
+            new CreateInstructionTabCommand("Настройка роутера", "текст", 10),
+            CancellationToken.None
+        );
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal("Настройка роутера", result.Value.Title);
+        Assert.Single(dbContext.InstructionTabs);
+    }
+
+    [Fact]
+    public async Task Update_ReplacesFields()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var tab = InstructionTab.Create("Старое", "старый текст", 10);
+        dbContext.InstructionTabs.Add(tab);
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        var handler = new UpdateInstructionTabCommandHandler(dbContext);
+
+        var result = await handler.Handle(
+            new UpdateInstructionTabCommand(tab.Id, "Новое", "новый текст", 20),
+            CancellationToken.None
+        );
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal("Новое", result.Value.Title);
+        Assert.Equal("новый текст", result.Value.Body);
+        Assert.Equal(20, result.Value.SortOrder);
+    }
+
+    [Fact]
+    public async Task Update_WhenTabMissing_ReturnsNotFound()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var handler = new UpdateInstructionTabCommandHandler(dbContext);
+
+        var result = await handler.Handle(
+            new UpdateInstructionTabCommand(Guid.NewGuid(), "Новое", "текст", 10),
+            CancellationToken.None
+        );
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal(InstructionErrors.TabNotFound, result.Error);
+    }
+
+    [Fact]
+    public async Task Delete_RemovesTab()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var tab = InstructionTab.Create("Удалить меня", "текст", 10);
+        dbContext.InstructionTabs.Add(tab);
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        var handler = new DeleteInstructionTabCommandHandler(dbContext);
+
+        var result = await handler.Handle(
+            new DeleteInstructionTabCommand(tab.Id),
+            CancellationToken.None
+        );
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        Assert.True(result.IsSuccess);
+        Assert.Empty(dbContext.InstructionTabs);
+    }
+
+    [Fact]
+    public async Task Delete_WhenTabMissing_ReturnsNotFound()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var handler = new DeleteInstructionTabCommandHandler(dbContext);
+
+        var result = await handler.Handle(
+            new DeleteInstructionTabCommand(Guid.NewGuid()),
+            CancellationToken.None
+        );
+
+        Assert.False(result.IsSuccess);
+        Assert.Equal(InstructionErrors.TabNotFound, result.Error);
+    }
+}

backend/tests/PnvPanel.Application.Tests/Admin/Instructions/UpdateInstructionIntroCommandHandlerTests.cs

@@ -0,0 +1,49 @@
+using PnvPanel.Application.Admin.Instructions;
+using PnvPanel.Application.Tests.TestSupport;
+using PnvPanel.Domain.Instructions;
+using Xunit;
+
+namespace PnvPanel.Application.Tests.Admin.Instructions;
+
+public class UpdateInstructionIntroCommandHandlerTests
+{
+    [Fact]
+    public async Task Handle_WhenNoIntroExists_CreatesIt()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var handler = new UpdateInstructionIntroCommandHandler(dbContext);
+
+        var result = await handler.Handle(
+            new UpdateInstructionIntroCommand("Новый текст"),
+            CancellationToken.None
+        );
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal("Новый текст", result.Value.Body);
+        Assert.Single(dbContext.InstructionIntros);
+    }
+
+    [Fact]
+    public async Task Handle_WhenIntroExists_UpdatesItInPlace()
+    {
+        using var dbContext = InMemoryDbContextFactory.Create();
+        var intro = InstructionIntro.Create("Старый текст");
+        dbContext.InstructionIntros.Add(intro);
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        var handler = new UpdateInstructionIntroCommandHandler(dbContext);
+
+        var result = await handler.Handle(
+            new UpdateInstructionIntroCommand("Обновлённый текст"),
+            CancellationToken.None
+        );
+        await dbContext.SaveChangesAsync(CancellationToken.None);
+
+        Assert.True(result.IsSuccess);
+        Assert.Equal(intro.Id, result.Value.Id);
+        Assert.Equal("Обновлённый текст", result.Value.Body);
+        // Не создаётся вторая строка — обновляется существующая (singleton).
+        Assert.Single(dbContext.InstructionIntros);
+    }
+}

backend/tests/PnvPanel.Application.Tests/Admin/Maintenance/FactoryResetCommandHandlerTests.cs

@@ -21,6 +21,8 @@ public class FactoryResetCommandHandlerTests
     private readonly IFileStorage _fileStorage = Substitute.For<IFileStorage>();
     private readonly IClientAppCatalogSeeder _catalogSeeder =
         Substitute.For<IClientAppCatalogSeeder>();
+    private readonly IInstructionIntroSeeder _instructionIntroSeeder =
+        Substitute.For<IInstructionIntroSeeder>();
 
     [Fact]
     public async Task Handle_WipesEverythingExceptCurrentAdminAndSystemRoles()
@@ -101,6 +103,7 @@ public class FactoryResetCommandHandlerTests
             _gateway,
             _fileStorage,
             _catalogSeeder,
+            _instructionIntroSeeder,
             currentUser
         );
 
@@ -140,5 +143,6 @@ public class FactoryResetCommandHandlerTests
             );
         await _fileStorage.Received(1).DeleteAsync("stored-name", Arg.Any<CancellationToken>());
         await _catalogSeeder.Received(1).SeedIfEmptyAsync(Arg.Any<CancellationToken>());
+        await _instructionIntroSeeder.Received(1).SeedIfEmptyAsync(Arg.Any<CancellationToken>());
     }
 }