Enhance school creation and staffing management with native language support

- Updated protocol documentation to include `nativeLanguages` in `nameSets` and added `nativeLanguage` to school creation options.
- Enhanced the UI for school creation to allow selection of native languages, improving user experience.
- Revised API interfaces to accommodate new native language features, ensuring proper data handling.
- Improved localization strings to support new native language functionalities in both English and Russian.
- Updated tests to validate the new native language features and ensure robust functionality in staffing scenarios.

tests/HSchool.AppHost.Tests/SchoolApiTests.cs

@@ -160,6 +160,11 @@ public class SchoolApiTests(AppHostFixture fixture)
         Assert.Equal("yard", ru.DefaultMap.Territory?.Id);
         Assert.Equal("Славянский", Assert.Single(ru.NameSets, set => set.DefName == "Slavic").Label);
         Assert.Equal("Slavic", Assert.Single(en.NameSets, set => set.DefName == "Slavic").Label);
+        var slavic = Assert.Single(ru.NameSets, set => set.DefName == "Slavic");
+        Assert.Equal(
+            ["RussianLanguage", "BelarusianLanguage", "UkrainianLanguage"],
+            slavic.NativeLanguages.Select(language => language.DefName).ToArray());
+        Assert.Equal("Белорусский", Assert.Single(slavic.NativeLanguages, language => language.DefName == "BelarusianLanguage").Label);
         Assert.Equal("Начальные классы", Assert.Single(ru.Subjects, subject => subject.DefName == "PrimarySchool").Label);
         Assert.Equal("Primary", Assert.Single(en.Subjects, subject => subject.DefName == "PrimarySchool").Label);
         var classroom = Assert.Single(ru.Rooms, room => room.DefName == "Classroom");
@@ -287,6 +292,27 @@ public class SchoolApiTests(AppHostFixture fixture)
         Assert.Equal("unknown-name-set", await ProblemCodeAsync(response));
     }
 
+    [Fact]
+    public async Task CreateSchool_WithAnUnknownNativeLanguage_IsRejected()
+    {
+        using var client = fixture.App.CreateHttpClient("server");
+        await ResetAsync(client);
+
+        using var response = await client.PostAsJsonAsync(
+            "/api/schools",
+            new
+            {
+                name = "Чужой язык",
+                startDate = ExpectedDefaultStart,
+                nameSetId = "Slavic",
+                nativeLanguage = "Klingon",
+            },
+            TestContext.Current.CancellationToken);
+
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+        Assert.Equal("unknown-native-language", await ProblemCodeAsync(response));
+    }
+
     [Fact]
     public async Task CreateSchool_WithACustomConnectedMap_Succeeds()
     {
@@ -417,7 +443,7 @@ public class SchoolApiTests(AppHostFixture fixture)
         IReadOnlyList<DefInfoResponse> Floors,
         IReadOnlyList<RoomInfoResponse> Rooms,
         IReadOnlyList<DefInfoResponse> Things,
-        IReadOnlyList<DefInfoResponse> NameSets,
+        IReadOnlyList<NameSetInfoResponse> NameSets,
         IReadOnlyList<SubjectInfoResponse> Subjects,
         DayFrameResponse? DayFrame,
         IReadOnlyList<HolidayInfoResponse> Holidays,
@@ -425,6 +451,11 @@ public class SchoolApiTests(AppHostFixture fixture)
 
     private sealed record DefInfoResponse(string DefName, string Label);
 
+    private sealed record NameSetInfoResponse(
+        string DefName,
+        string Label,
+        IReadOnlyList<DefInfoResponse> NativeLanguages);
+
     private sealed record RoomInfoResponse(
         string DefName,
         string Label,