feat(tui): codex-style input, history, bang commands, single-line status bar

- Arrow-key input history (up/down with multiline awareness)
- Bang shell commands via ! prefix (requires --yolo)
- Codex-style input bar with mode indicator (R/Y/⌘)
- Command palette virtual scrolling
- Multiline input viewport fix
- Merged model pills + footer into single status line
- Removed shift+enter (wait for TUI library support)
- Removed default footer hints

internal/session/manager_test.go

@@ -109,6 +109,18 @@ func TestManagerRejectsUnknownModelAndThinking(t *testing.T) {
 	}
 }
 
+func TestManagerExposesModelCommandCandidates(t *testing.T) {
+	manager, _, _ := testManager(t)
+	models := manager.AvailableModels()
+	if len(models) != 2 || models[0] != "model-a" || models[1] != "model-b" {
+		t.Fatalf("AvailableModels() = %v", models)
+	}
+	models[0] = "mutated"
+	if got := manager.AvailableModels()[0]; got != "model-a" {
+		t.Fatalf("mutation leaked: %q", got)
+	}
+}
+
 func TestManagerSaveAndResume(t *testing.T) {
 	manager, assistant, _ := testManager(t)