Feat: add persisted account theme settings

Backend/internal/bootstrap/service_test.go

@@ -206,6 +206,13 @@ func TestEnsureBootstrapPOSIXSkeletonInitializesEmptyRoot(t *testing.T) {
 	if personalSettings["slug"] != "ronald" {
 		t.Fatalf("expected personal slug ronald, got %#v", personalSettings["slug"])
 	}
+	personalTheme, ok := personalSettings["theme"].(map[string]any)
+	if !ok {
+		t.Fatalf("expected personal settings to contain theme object, got %#v", personalSettings)
+	}
+	if personalTheme["presetId"] != defaultThemePresetID {
+		t.Fatalf("expected personal theme preset %s, got %#v", defaultThemePresetID, personalTheme["presetId"])
+	}
 
 	personalHome := readStructuredFileForTest[map[string]any](t, filepath.Join(rootPath, "users", "personals", "personal-ronald", posixHomeFileName))
 	if personalHome["type"] != "personal-home" {
@@ -277,6 +284,39 @@ func TestCreateProjectHierarchyFolderOnDiskCreatesExpectedFolderShape(t *testing
 	}
 }
 
+func TestPersonalSettingsPathForDisplayName(t *testing.T) {
+	path := personalSettingsPathForDisplayName(" Ronald ")
+	if path != "users/personals/personal-ronald/settings.cbor" {
+		t.Fatalf("unexpected personal settings path: %s", path)
+	}
+}
+
+func TestApplyThemePresetToSettingsPreservesExistingFields(t *testing.T) {
+	settings := map[string]any{
+		"type": "personal",
+		"slug": "ronald",
+		"theme": map[string]any{
+			"density": "comfortable",
+		},
+	}
+
+	updated := applyThemePresetToSettings(settings, "moku-default")
+
+	if updated["type"] != "personal" {
+		t.Fatalf("expected type personal, got %#v", updated["type"])
+	}
+	theme, ok := updated["theme"].(map[string]any)
+	if !ok {
+		t.Fatalf("expected theme object, got %#v", updated["theme"])
+	}
+	if theme["presetId"] != "moku-default" {
+		t.Fatalf("expected presetId moku-default, got %#v", theme["presetId"])
+	}
+	if theme["density"] != "comfortable" {
+		t.Fatalf("expected density to be preserved, got %#v", theme["density"])
+	}
+}
+
 func TestCreateProjectTreeFolderOnDiskCreatesExpectedFolderShape(t *testing.T) {
 	rootPath := filepath.Join(t.TempDir(), "POSIX")
 	service := NewService(nil, rootPath)