feat(gui): hand-rolled winit loop for true window-hide on Wayland

Replace eframe::run_native with a winit ApplicationHandler + glutin +
egui_glow loop so "keep running in the tray" can genuinely hide the
window. winit's set_visible(false) is a deliberate no-op on Wayland
(xdg-shell has no unmap-but-keep-alive request), so the only way to hide
a toplevel is to destroy its surface: hide-to-tray now drops the Window +
GL surface (parking the GL context as not-current) and a tray click
recreates them and makes the context current again. The GL context,
glutin display/config, egui_glow painter (uploaded textures), and
egui-winit state (clipboard) all persist across the cycle — only the OS
window and its surface churn.

Wakeups route through winit's EventLoopProxy (the new Waker, and the
tray) instead of egui's repaint callback, so a child event or tray click
wakes the loop even while the window is dropped and no frame is running —
keeping viewer join/leave notifications and the tray tooltip live while
hidden. Removes the old Wayland minimize-to-tray fallback (window stayed
in the taskbar); hide is now uniform on Wayland and X11.

Deps: winit/glutin/glutin-winit/egui_glow promoted to direct (gui-gated,
optional) — all already transitive via eframe, so no new crates. winit's
default features minus wayland-csd-adwaita, so sctk-adwaita/tiny-skia/
ttf-parser aren't pulled for a CSD fallback titlebar (KWin draws
server-side decorations, and eframe never had CSD either).

Verified end-to-end on KWin Wayland: launch->render; close->window AND
taskbar entry gone (true hide, process stays alive); tray activate->
window + GL surface recreated and renders; tray quit->clean exit; stderr
clean throughout. cargo test --features gui: 15 pass; clippy clean;
headless dependency tree unchanged.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -87,6 +87,12 @@ share code appears with a copy button. Connected viewers are listed with a
 **Kick** button each, and a desktop notification fires as they join or leave.
 View: paste a code, pick mpv or VLC, click **Connect** and the player launches.
 
+A system-tray icon shows current status. **Settings → "Keep running in the
+tray when I close the window"** (off by default) makes the close button hide
+the window — truly, by dropping it — while any active stream keeps running in
+the child; reopen it from the tray. (Plain close still quits when the option is
+off, or when no system tray is present.)
+
 The window is a thin driver — it runs the same headless `pixelpass` as a
 child process and reads its event stream, so the GUI is purely additive and
 the capture machinery is untouched by it. On a build without the feature,