feat(client-linux): in-process GL presenter — hardware decode ships on the Steam Deck

VAAPI decode stays; what changes is who touches the YUV. The direct path hands
the NV12 dmabuf (tiled AMD modifier since Mesa 25.1) to GdkDmabufTexture, and
GTK's tiled-NV12 import renders corrupt/gray/washed-out on the Deck. Moonlight
and mpv are clean on the same box because they import the dmabuf into their own
EGL context and convert with their own shader — video_gl.rs is that
architecture for the GTK client: per-plane EGLImages (R8 + GR88, modifier
passed through) → our YUV→RGB shader (matrix/range from the stream's CICP
signaling, unit-tested) → RGBA texture in a GdkGLContext-shared context →
fence-synced GdkGLTexture. GTK composites plain RGBA; no YUV negotiation, no
compositor CSC.

The Deck's decoder default flips back to hardware (the software stopgap is
gone); desktops keep the direct dmabuf path (offload/scan-out eligible).
PUNKTFUNK_PRESENT=direct|gl overrides either way. New failure ladder: GL
converter init failure or a convert-error streak raises a shared flag and the
session pump demotes the decoder to software with a keyframe re-request — the
same mechanism also closes the old silent-black-screen gap where a rejected
dmabuf import had no recovery at all.

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

clients/linux/Cargo.toml

@@ -31,6 +31,9 @@ pipewire = "0.9"
 # Gamepads: capture + feedback (full DualSense fidelity — touchpad/motion/triggers/LEDs
 # need the hidapi driver).
 sdl3 = { version = "0.18", features = ["hidapi"] }
+# The VAAPI GL presenter (video_gl.rs): EGL dmabuf import into a GDK-shared context, dlopened
+# at runtime (`dynamic`) so GPU-less boxes and the software path never touch libEGL.
+khronos-egl = { version = "6", features = ["dynamic"] }
 
 mdns-sd = "0.20"
 # Game-library fetch from the host's management API over mTLS + fingerprint pinning.