fix(linux/vdisplay): KWin virtual outputs stream above 60 Hz via sacrificial-birth renegotiation

KWin's ScreenCastStream builds its PipeWire format offer — including the
maxFramerate cap it actively throttles delivery to — ONCE at stream
creation, when the virtual output sits at its hardcoded birth 60 Hz. A
kscreen custom-mode change afterwards updates the OUTPUT (readback says
240) but never the offer, so every consumer negotiates max=60 and the
stream delivers 60 (pw-dump-verified on KWin 6.6.4). The only path that
rebuilds the offer is the stream's own resize handling: a source SIZE
change while recording re-runs buildFormats — picking up the output's
current refresh — and renegotiates the live stream.

So above 60 Hz, birth the output at a sacrificial height (+16), then
install + select the real WxH@hz custom mode: the first frame recorded
after the consumer connects triggers KWin's resize path, which renegotiates
the live stream to WxH@hz. The capturer holds (requeues) buffers until the
negotiated size matches — new expect_exact_dims plumbing VirtualOutput →
registry (fresh creates only) → open_virtual_output → a self-disarming
gate in the process callback — bounded by a 3 s deadline that accepts the
producer's dims rather than wedging the session into the first-frame
retry loop. set_custom_refresh reads back the full active mode; a size
reject (pre-6.6 KWin) recreates plain at the real size @60.

Every kscreen operation now addresses the output by its NUMERIC id,
resolved by matching the managed name-prefix AND the just-created birth
size (newest id wins): a mode-switch supersede reuses the per-slot output
NAME (deliberately, for KWin's per-name config persistence) while the
superseded sibling is still alive, and name addressing hit the FIRST
match = the OLD output — on-glass that resized the live session's display
out from under it (wrong-res/black), read the old output back as 'mode
applied', and set the old output primary while the replacement starved at
its birth mode.

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

crates/pf-capture/src/lib.rs

@@ -453,6 +453,7 @@ pub fn open_virtual_output(
     allow_zerocopy: bool,
     want_444: bool,
     policy: ZeroCopyPolicy,
+    expect_exact_dims: bool,
 ) -> Result<Box<dyn Capturer>> {
     linux::PortalCapturer::from_virtual_output(
         remote_fd,
@@ -462,6 +463,7 @@ pub fn open_virtual_output(
         allow_zerocopy,
         want_444,
         policy,
+        expect_exact_dims,
     )
     .map(|c| Box::new(c) as Box<dyn Capturer>)
 }