fix(tui): update picker_test for switchProviderModel 4-value return

#568 added a bool return to switchProviderModel (model, string, bool,
tea.Cmd) and updated every call site except picker_test.go:771, which
still assigned three values. That broke the internal/tui test build
and turned Smoke red on main. Add the missing receiver here.

Author: Vasanthdev2004

internal/tui/picker_test.go

@@ -768,7 +768,7 @@ func TestSwitchProviderModelRecordsRecentHistory(t *testing.T) {
 		},
 	})
 
-	next, status, _ := m.switchProviderModel("ollama", "kimi-k2.7-code:cloud")
+	next, status, _, _ := m.switchProviderModel("ollama", "kimi-k2.7-code:cloud")
 	wantStatus := "Model\nSwitched to ollama · kimi-k2.7-code:cloud"
 	if status != wantStatus {
 		t.Fatalf("switchProviderModel() status = %q, want %q (a mismatch here means the switch itself failed, not the recentModels assertion below)", status, wantStatus)