feat(i18n): add LocaleStore folder discovery

tests/ClaudeDo.Localization.Tests/LocaleStoreTests.cs

@@ -0,0 +1,38 @@
+using ClaudeDo.Localization;
+
+namespace ClaudeDo.Localization.Tests;
+
+public class LocaleStoreTests
+{
+    private static string WriteTempLocales(params (string file, string json)[] files)
+    {
+        var dir = Path.Combine(Path.GetTempPath(), "loc_" + Guid.NewGuid().ToString("N"));
+        Directory.CreateDirectory(dir);
+        foreach (var (file, json) in files)
+            File.WriteAllText(Path.Combine(dir, file), json);
+        return dir;
+    }
+
+    [Fact]
+    public void Load_discovers_all_json_files()
+    {
+        var dir = WriteTempLocales(
+            ("en.json", """{ "metadata": { "code": "en", "name": "English" }, "a": { "b": "x" } }"""),
+            ("de.json", """{ "metadata": { "code": "de", "name": "Deutsch" }, "a": { "b": "y" } }"""));
+
+        var store = LocaleStore.Load(dir);
+
+        Assert.Equal(2, store.Available.Count);
+        Assert.True(store.TryGet("en", out var en));
+        Assert.Equal("x", en!.Strings["a.b"]);
+        Assert.True(store.TryGet("de", out var de));
+        Assert.Equal("Deutsch", de!.Name);
+    }
+
+    [Fact]
+    public void Load_returns_empty_when_folder_missing()
+    {
+        var store = LocaleStore.Load(Path.Combine(Path.GetTempPath(), "does_not_exist_" + Guid.NewGuid()));
+        Assert.Empty(store.Available);
+    }
+}