qt: parity batch 3 — quit-timer-on-natural-close + bell fallback (B1, I9)

Two fixes from PARITY.md:

  B1 — quit-after-last-window-closed-delay now fires when the user
  closes the last window via the WM, not only when libghostty issues
  the QUIT_TIMER action. ~MainWindow detects the empty-s_windows +
  delay-configured case and arms handleQuitTimer(true), then returns
  before tearing down s_app/s_config so the timer can fire on a still-
  alive process. newWindow() cancels the timer so a new window opened
  during the delay window keeps the process alive (mirrors the GTK
  startQuitTimer/stopQuitTimer wiring at application.zig:820-862).
  Previously, with delay > 0, closing the final window via the title-
  bar X kept the process alive forever — quitOnLastWindowClosed was
  intentionally off, but nothing else triggered the timer.

  I9 — bell-features fallback only applies on a real config-get
  failure. The prior code initialised features=BellAttention then
  unconditionally overwrote it from configGet's out param. If a user
  set bell-features = (no flags), configGet wrote 0 and we honored
  that — fine. But the fallback semantics were ambiguous: a future
  ABI drift causing configGet to fail would still leave features
  set to BellAttention, while users who explicitly turned off all
  bell features would get nothing. Now: read configGet's return,
  fall back to BellAttention only when it returns false. Honors
  explicit-zero, falls back only on actual decode failure.

Note: B44 (quick-terminal-position = center) was already implemented
at MainWindow.cpp:766; the audit report was wrong on that one.
Removed from the tracker.

Co-Authored-By: claude-flow <ruv@ruv.net>

qt/src/MainWindow.cpp

@@ -104,6 +104,17 @@ MainWindow::~MainWindow() {
   qDeleteAll(m_surfaces);
   m_surfaces.clear();
 
+  // If this was the last window and a quit delay is configured, arm
+  // the natural-close quit timer instead of tearing down immediately.
+  // Qt's setQuitOnLastWindowClosed is off (we did that in initialize
+  // so the delay can run), so without this the process would stay
+  // alive forever after closing the final window via the WM.
+  // Mirrors GTK's application.zig:820-862 startQuitTimer wiring.
+  if (s_windows.isEmpty() && s_quitDelayMs > 0) {
+    handleQuitTimer(true);
+    return;  // keep s_app + s_config alive until the timer fires
+  }
+
   // The shared app and config outlive every window but the last.
   if (s_windows.isEmpty()) {
     if (s_frameTimer) {
@@ -295,6 +306,12 @@ bool MainWindow::initialize() {
 }
 
 MainWindow *MainWindow::newWindow(ghostty_surface_t parent) {
+  // If the natural-close quit timer is running (because the last
+  // window was closed and we're inside the configured delay), cancel
+  // it now: the process is no longer headless. macOS/GTK do the
+  // same.
+  if (s_quitTimer) handleQuitTimer(false);
+
   auto *w = new MainWindow;
   w->setAttribute(Qt::WA_DeleteOnClose);  // self-destruct when closed
   w->m_firstTabParent = parent;           // first tab inherits from `parent`
@@ -957,9 +974,15 @@ void MainWindow::moveTab(int amount) {
 
 void MainWindow::ringBell(GhosttySurface *surface) {
   // bell-features is a packed struct returned by ghostty_config_get as
-  // a bitfield (see BellFeature in Util.h).
-  unsigned int features = BellAttention;  // fallback if config-get fails
-  configGet(s_config, &features, "bell-features");
+  // a bitfield (see BellFeature in Util.h). If the config-get call
+  // itself fails (e.g. an ABI drift between Qt frontend and libghostty
+  // dropping the field), use BellAttention as a sane minimum fallback.
+  // If config-get succeeds with features=0, the user explicitly opted
+  // out of every bell feature and we honor that.
+  unsigned int features = 0;
+  if (!configGet(s_config, &features, "bell-features")) {
+    features = BellAttention;
+  }
   if (features & BellAttention) QApplication::alert(this);
   if (features & BellSystem) QApplication::beep();
   if (features & BellAudio) playBellAudio();