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/SchoolStore.cs

@@ -26,6 +26,11 @@ internal sealed class SchoolSave
 
     public MapLayout? Map { get; init; }
 
+    public string? CountryId { get; init; }
+
+    public string? ClimatePresetId { get; init; }
+
+    /// <summary>Legacy field. Format 2 and older; mapped to <see cref="CountryId"/> on load.</summary>
     public string? NameSetId { get; init; }
 
     public string? NativeLanguage { get; init; }
@@ -42,7 +47,7 @@ internal sealed record SchoolSaveIndex(int NextId);
 /// </summary>
 internal sealed class SchoolStore
 {
-    public const int CurrentFormat = 2;
+    public const int CurrentFormat = 3;
 
     private const string IndexFileName = "index.json";
 
@@ -178,6 +183,8 @@ internal sealed class SchoolStore
                     SpeedIndex = save.SpeedIndex,
                     ModIds = save.ModIds,
                     Map = save.Map,
+                    CountryId = save.CountryId,
+                    ClimatePresetId = save.ClimatePresetId,
                     NameSetId = save.NameSetId,
                     NativeLanguage = save.NativeLanguage,
                     Presence = save.Presence,
@@ -194,11 +201,40 @@ internal sealed class SchoolStore
     }
 
     /// <summary>
-    /// Named upgrade seam for saves older than <see cref="CurrentFormat"/>. Empty on purpose:
-    /// missing fields already default and extra fields are ignored. Put a migration here when a
-    /// format bump actually needs one.
+    /// Format 2 stored a name set. Slavic becomes Russia; any other id is tried as a country
+    /// (the example pack kept its defName). Climate is filled on the worker from the country's
+    /// first preset so the file is not rewritten until the school saves itself.
     /// </summary>
-    internal static SchoolSave UpgradeOlderSave(SchoolSave save) => save;
+    internal static SchoolSave UpgradeOlderSave(SchoolSave save)
+    {
+        if (!string.IsNullOrWhiteSpace(save.CountryId))
+        {
+            return save;
+        }
+
+        var countryId = save.NameSetId switch
+        {
+            "Slavic" or null or "" => "Russia",
+            _ => save.NameSetId,
+        };
+
+        return new SchoolSave
+        {
+            Format = save.Format,
+            Id = save.Id,
+            Name = save.Name,
+            GameTime = save.GameTime,
+            Running = save.Running,
+            SpeedIndex = save.SpeedIndex,
+            ModIds = save.ModIds,
+            Map = save.Map,
+            CountryId = countryId,
+            ClimatePresetId = save.ClimatePresetId,
+            NameSetId = save.NameSetId,
+            NativeLanguage = save.NativeLanguage,
+            Presence = save.Presence,
+        };
+    }
 
     public void Save(SchoolSave save)
     {