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.People/CountryClimate.cs

@@ -0,0 +1,26 @@
+namespace HSchool.People;
+
+/// <summary>
+/// A country lists climate presets; the school rolls one at birth from the school seed.
+/// Reloads without a stored pick take the first listed preset so old saves stay put.
+/// </summary>
+public static class CountryClimate
+{
+    public static string? Pick(CountryDef country, int schoolSeed, bool rollIfOmitted)
+    {
+        ArgumentNullException.ThrowIfNull(country);
+        var presets = country.ClimatePresets;
+        if (presets.Count == 0)
+        {
+            return null;
+        }
+
+        if (!rollIfOmitted || presets.Count == 1)
+        {
+            return presets[0];
+        }
+
+        var rng = new Random(Seed.ForSchool(schoolSeed, Seed.ClimatePresetSalt));
+        return presets[rng.Next(presets.Count)];
+    }
+}