fix(stats): decode stage measures GPU completion; Alt+Enter fullscreen alias

The Vulkan path's receive_frame returns at SUBMISSION (~0.1 ms) — the
hardware decodes asynchronously, so the decode stat was truthful but
measured the wrong boundary. The pump now ships the frame to the
presenter FIRST, then waits the frame's timeline fence (vkWaitSemaphores
resolved through the shared device's proc chain) and stamps
received→decode-COMPLETE — true NVDEC time at zero pipeline cost, since
the presenter's own GPU wait is what actually gates sampling. Software/
VAAPI keep their synchronous stamps.

Also: Alt+Enter joins F11 as the fullscreen toggle (some keyboards' Fn
layer sends a media key for plain F11 — observed on glass as
'F11 only works with shift'); the shell's shortcuts panel lists both.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

scripts/headless/portals.conf

@@ -1,5 +1,15 @@
 # ~/.config/xdg-desktop-portal/sway-portals.conf  (xdg-desktop-portal 1.18+ format)
-# Force the wlroots backend to service ScreenCast; gtk handles the rest.
+# Route ScreenCast to the right wlr-family backend; gtk handles the rest.
+#
+# A desktop-specific section (matched against XDG_CURRENT_DESKTOP, which the host sets per session —
+# `sway` for sway/river, `Hyprland` for Hyprland) wins over [preferred]. So sway hosts capture
+# through xdg-desktop-portal-wlr (xdpw) and Hyprland hosts through xdg-desktop-portal-hyprland
+# (xdph) — each the backend the host actually steers.
 [preferred]
 default=gtk
 org.freedesktop.impl.portal.ScreenCast=wlr
+
+# Hyprland: XDG_CURRENT_DESKTOP=Hyprland → xdph services ScreenCast (the host steers its custom
+# picker via ~/.config/hypr/xdph.conf). See docs/hyprland.
+[Hyprland]
+org.freedesktop.impl.portal.ScreenCast=hyprland