Stabilisation quick fixes: orderly close, visible version and update band, chat pop-ups on, Windows shaders and hwdec, render logs

- Close: hide the window, dispose every player, thumbnail job and the
  sound engine, leave, then close normally; Linux runner _exit (the
  NVIDIA EGL exit handler crashed 10/10 closes, 0/41 now); Windows tears
  down inside the message loop, then TerminateProcess; watchdogs.
- Version under the Settings tab; an update band instead of a dot,
  never over a video; checks at start and every 4 hours.
- Chat pop-ups default to All again.
- Shader read-back compared as a list (old mpv joins with ','), so
  Windows stops turning shaders off; Windows hwdec auto-copy.
- Render diagnostics (`mpv: render` lines); RAM-only demuxer cache pin
  silences the file-cache warning; a volume readout test.

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

apps/desktop/windows/runner/flutter_window.cpp

@@ -1,11 +1,30 @@
 #include "flutter_window.h"
 
+#include <cstdio>
 #include <optional>
+#include <thread>
 
 #include <flutter/standard_method_codec.h>
 
 #include "flutter/generated_plugin_registrant.h"
 
+namespace {
+
+// Ends the process after |ms| whatever is still running: the app's close
+// (lib/src/platform/app_shutdown.dart) is bounded, but a native teardown
+// can block for good (media_kit_video's ~VideoOutput waits on a texture
+// callback the stopped engine never sends). The process must never stay
+// behind a hidden window.
+void ExitAfter(DWORD ms) {
+  std::thread([ms] {
+    ::Sleep(ms);
+    fflush(nullptr);
+    ::TerminateProcess(::GetCurrentProcess(), 0);
+  }).detach();
+}
+
+}  // namespace
+
 FlutterWindow::FlutterWindow(const flutter::DartProject& project)
     : project_(project) {}
 
@@ -60,6 +79,8 @@ bool FlutterWindow::OnCreate() {
 }
 
 void FlutterWindow::OnDestroy() {
+  // The engine and the plugins go now; the app released its players first.
+  ExitAfter(3000);
   window_channel_ = nullptr;
   if (flutter_controller_) {
     flutter_controller_ = nullptr;
@@ -72,6 +93,13 @@ LRESULT
 FlutterWindow::MessageHandler(HWND hwnd, UINT const message,
                               WPARAM const wparam,
                               LPARAM const lparam) noexcept {
+  // A close request starts the app's close (players, leave), at most a
+  // few seconds; past 15 s the process ends anyway.
+  if (message == WM_CLOSE && !close_requested_) {
+    close_requested_ = true;
+    ExitAfter(15000);
+  }
+
   // Give Flutter, including plugins, an opportunity to handle window messages.
   if (flutter_controller_) {
     std::optional<LRESULT> result =