Add virtual model support for multi-key expansion

Virtual models generated from multi-key expansion are now marked and
filtered during config persistence. Virtual models display with a badge
in the UI and cannot be set as default.

pkg/config/config_test.go

@@ -391,6 +391,65 @@ func TestSaveConfig_PreservesDisabledTelegramPlaceholder(t *testing.T) {
 	}
 }
 
+// TestSaveConfig_FiltersVirtualModels verifies that SaveConfig does not write
+// virtual models (generated by expandMultiKeyModels) to the config file.
+func TestSaveConfig_FiltersVirtualModels(t *testing.T) {
+	tmpDir := t.TempDir()
+	path := filepath.Join(tmpDir, "config.json")
+
+	cfg := DefaultConfig()
+
+	// Manually add a virtual model to ModelList (simulating what expandMultiKeyModels does)
+	primaryModel := &ModelConfig{
+		ModelName: "gpt-4",
+		Model:     "openai/gpt-4o",
+		apiKeys:   []string{"key1"},
+	}
+	virtualModel := &ModelConfig{
+		ModelName: "gpt-4__key_1",
+		Model:     "openai/gpt-4o",
+		apiKeys:   []string{"key2"},
+		isVirtual: true,
+	}
+	cfg.ModelList = []*ModelConfig{primaryModel, virtualModel}
+
+	// SaveConfig should filter out virtual models
+	if err := SaveConfig(path, cfg); err != nil {
+		t.Fatalf("SaveConfig failed: %v", err)
+	}
+
+	// Reload and verify
+	reloaded, err := LoadConfig(path)
+	if err != nil {
+		t.Fatalf("LoadConfig failed: %v", err)
+	}
+
+	// Should only have the primary model, not the virtual one
+	if len(reloaded.ModelList) != 1 {
+		t.Fatalf("expected 1 model after reload, got %d", len(reloaded.ModelList))
+	}
+
+	if reloaded.ModelList[0].ModelName != "gpt-4" {
+		t.Errorf("expected model_name 'gpt-4', got %q", reloaded.ModelList[0].ModelName)
+	}
+
+	// Verify virtual model was not persisted
+	for _, m := range reloaded.ModelList {
+		if m.ModelName == "gpt-4__key_1" {
+			t.Errorf("virtual model gpt-4__key_1 should not have been saved")
+		}
+	}
+
+	// Verify the saved file does not contain the virtual model name
+	data, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("ReadFile failed: %v", err)
+	}
+	if strings.Contains(string(data), "gpt-4__key_1") {
+		t.Errorf("saved config should not contain virtual model name 'gpt-4__key_1'")
+	}
+}
+
 // TestConfig_Complete verifies all config fields are set
 func TestConfig_Complete(t *testing.T) {
 	cfg := DefaultConfig()