Replace selectable name sets with a country that owns names and climate presets.

Create picks a country; climate is rolled from the school seed and stored. Old Slavic saves lift as Russia.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/HSchool.Server/Game/GameCommand.cs

@@ -16,7 +16,7 @@ internal abstract record GameCommand
         DateTime StartDate,
         IReadOnlyList<string>? ExtraModIds,
         MapLayout? Map,
-        string? NameSetId,
+        string? CountryId,
         string? NativeLanguage,
         int? Seed,
         TaskCompletionSource<SchoolCreationOutcome> Result) : GameCommand;