Fix Windows player: kiosk lockdown, robust video transitions, keep-awake

- Production/kiosk mode: exit_on_escape=0, window-close guard, Ctrl+C
  ignore, Alt+F4/Alt+Tab/Win/Ctrl+Esc keyboard hook (Windows)
- Robust video playback: async (non-blocking) ffpyplayer teardown,
  video progress watchdog (advance at true clip end), EOS re-entrancy
  guard, stale-advance guard, focus keeper for foreground retention
- Resume playback timer after Settings/exit popups close
- Windows keep-awake: SetThreadExecutionState + disable screensaver/
  lock screen (restored on exit)
- Always-on playback_trace.log for diagnosing transitions
- exe metadata: app_icon.ico + version_info.txt (publisher identity)

windows/development-track.md

@@ -76,7 +76,21 @@ in `windows/run_win.py`. All are covered except the one listed below:
   2. `_hide_overlay()` now calls **`_bring_chrome_to_front(proc)`** (new helper
      that enumerates `Chrome_WidgetWin_1/0` windows owned by the launched PID)
      instead of raising Kivy.
-- **Test:** exe rebuilt 2026-07-31 13:53; DLL set intact (28 DLLs incl. FFmpeg).
+- **Update (2026-07-31 15:42):** added **`--kiosk`** flag to the weblink launch
+  args so the browser opens in true kiosk mode (no UI/chrome, locks to screen).
+  Safe with the dedicated `--user-data-dir` — does not affect the user's normal
+  browser session.
+- **Update (2026-07-31 16:04):** replaced the fixed 1.0s overlay-hide timer with
+  **adaptive polling** (`_hide_overlay_when_chrome_ready`). The black overlay now
+  stays up until Chrome's window is actually detected on screen
+  (`_find_chrome_hwnd`), so the host desktop is never exposed during cold
+  starts / slow disk / GPU init. Falls back to Kivy after a 6s timeout.
+- **Update (2026-07-31 16:19):** added a **persistent `_Win32Backdrop`** — a
+  fullscreen black window created at player startup (`_Win32Backdrop.show()`)
+  placed at `HWND_BOTTOM` (below Kivy & the kiosk browser, above the desktop),
+  destroyed only on clean exit. Any browser load/unload gap now reveals clean
+  black instead of the host desktop.
+- **Test:** exe rebuilt 2026-07-31 16:19; DLL set intact (28 DLLs incl. FFmpeg).
 
 ### [BUG-012] Next widget never comes to foreground after weblink ends
 - **Status:** ✅ **Fixed — 2026-07-31**