Windows: every start ended itself after 3 s (1.3.0, 1.3.1)

Win32Window::Create calls Destroy() before it makes the window, which
ran FlutterWindow::OnDestroy and armed the 3 s exit timer at launch: the
window showed, then the process ended with code 0, no crash, no close
lines. The timer is only armed with an engine to tear down. Found and
fixed by Fun Maker's agent on Windows (a debugger caught the exit on the
timer's thread).

The smoke runs missed it (they closed at ~4 s anyway): the app now stays
up 10 s, and the scripts require 'closing' and 'quitting' from its own
close.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/DEVELOPMENT.md

@@ -210,10 +210,12 @@ updater tests, the release build and the close smoke run on that build
 `STARSYNC_SMOKE=<clip>` (a 5 s clip from ffmpeg, else a WAV the script
 writes) under its own profile (`STARSYNC_PROFILE=smoke`), opens the clip
 in a player with a video output through the media pipeline
-(`platform/smoke.dart`), plays a second and closes the normal way; the
-steps go to `STARSYNC_SMOKE_OUT` (`start`, `opened <ms> render=<mode>`,
-`closing`, or `skip` / `fail` with why). It fails when the app does not
-exit within 45 s or leaves a `starsync` process, skips with a warning
+(`platform/smoke.dart`), plays it, stays up 10 s from its start and
+closes the normal way; the steps go to `STARSYNC_SMOKE_OUT` (`start`,
+`opened <ms> render=<mode>`, `closing`, `quitting` just before the
+window closes, or `skip` / `fail` with why). It fails when the app ends
+by itself before `closing` or never reaches `quitting`, does not exit
+within 45 s or leaves a `starsync` process, skips with a warning
 when the runner cannot bring the app or its video output up, and prints
 the `smoke:`, `close:` and `mpv: render` lines of the app log.
 `tool/smoke_linux.sh` is the same on Linux (needs a display; after