fix(capture/mutter): stale-frame flashes + stuck input after disconnect on GNOME

Deep dive into the two GNOME-only host bugs (KWin/gamescope clean):

1. Stale-frame flashes (windows at old positions, typed text reverting):
   Mutter renders its virtual monitors DIRECTLY into the PipeWire buffer
   pool, and NVIDIA has no implicit dmabuf fencing — our zero-copy
   import raced the render and encoded each pool buffer's PREVIOUS
   contents. Fix, in order of preference:
   - Consumer-side PipeWire explicit sync (SPA_META_SyncTimeline): new
     drm_sync module (DRM timeline-syncobj wait/signal via raw ioctls,
     unit-tested incl. a live signal->wait round trip); announced
     post-format via update_params (the OBS pattern — at connect time
     the meta makes producers fail allocation, observed on KWin), with
     a blocks=3 Buffers filter so the producer's sync pod wins; acquire
     point awaited before any read (GPU import or CPU mmap), release
     point signaled on every path.
   - Where the producer can't do explicit sync (Mutter on NVIDIA today:
     no cogl sync_fd, "error alloc buffers"), a sticky fallback flips
     the capture to the synchronous CPU/shm path — Mutter's glReadPixels
     download orders against its render, so frames are correct by
     construction. First session pays one ~10 s probe+retry; later
     sessions go straight there. Validated live on home-worker-3
     (GNOME 50 + RTX 4090): clean fallback, 30 MB HEVC streamed.
   - Sync is only announced on Mutter sessions (new VirtualOutput.mutter
     tag): KWin+NVIDIA fails allocation when merely asked, and doesn't
     need it (verified unchanged: zero-copy CUDA import + 1.1 MB/10 s).
   PUNKTFUNK_EXPLICIT_SYNC=0 disables the probe outright.

2. Clicks wedged in the focused app after disconnect+reconnect: a client
   vanishing mid-press left keys/buttons latched in the compositor —
   Mutter keeps the destroyed EIS device's implicit grab and the focused
   app stops taking clicks until restarted. EiState now tracks held
   keys/buttons/touches (wire codes) and synthesizes releases through
   the normal inject path before the EIS connection goes away.

GNOME hosts on NVIDIA temporarily lose zero-copy (correctness over
throughput); the moment Mutter+driver gain working explicit sync, the
sync path engages automatically and zero-copy returns.

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

crates/punktfunk-host/src/vdisplay/gamescope.rs

@@ -83,6 +83,7 @@ impl VirtualDisplay for GamescopeDisplay {
             point_injector_at_eis();
             tracing::info!(node_id, "gamescope: attaching to existing PipeWire node");
             return Ok(VirtualOutput {
+                mutter: false,
                 node_id,
                 remote_fd: None,
                 preferred_mode: Some((mode.width, mode.height, mode.refresh_hz)),
@@ -107,6 +108,7 @@ impl VirtualDisplay for GamescopeDisplay {
             "gamescope virtual output ready"
         );
         Ok(VirtualOutput {
+            mutter: false,
             node_id,
             remote_fd: None,
             preferred_mode: Some((mode.width, mode.height, mode.refresh_hz)),
@@ -136,6 +138,7 @@ fn create_managed_session(client: &str, mode: Mode) -> Result<VirtualOutput> {
                 "gamescope session: reusing the running session (same mode — no Steam restart)"
             );
             return Ok(VirtualOutput {
+                mutter: false,
                 node_id,
                 remote_fd: None,
                 preferred_mode: Some((mode.width, mode.height, mode.refresh_hz)),
@@ -162,6 +165,7 @@ fn create_managed_session(client: &str, mode: Mode) -> Result<VirtualOutput> {
         "gamescope session: launched gamescope-session-plus at the client's mode"
     );
     Ok(VirtualOutput {
+        mutter: false,
         node_id,
         remote_fd: None,
         preferred_mode: Some((mode.width, mode.height, mode.refresh_hz)),

crates/punktfunk-host/src/vdisplay/kwin.rs

@@ -104,6 +104,7 @@ impl VirtualDisplay for KwinDisplay {
             mode.refresh_hz
         };
         Ok(VirtualOutput {
+            mutter: false,
             node_id,
             remote_fd: None,
             preferred_mode: Some((mode.width, mode.height, achieved_hz)),

crates/punktfunk-host/src/vdisplay/mutter.rs

@@ -85,6 +85,7 @@ impl VirtualDisplay for MutterDisplay {
             "Mutter virtual monitor ready"
         );
         Ok(VirtualOutput {
+            mutter: true,
             node_id,
             remote_fd: None,
             preferred_mode: Some((mode.width, mode.height, mode.refresh_hz)),

crates/punktfunk-host/src/vdisplay/wlroots.rs

@@ -123,6 +123,7 @@ impl VirtualDisplay for WlrootsDisplay {
             "sway headless output ready"
         );
         Ok(VirtualOutput {
+            mutter: false,
             node_id,
             remote_fd: Some(fd),
             preferred_mode: Some((mode.width, mode.height, mode.refresh_hz)),