fix(vdisplay/capture): channel-less sessions composite the pointer on a sticky-declared target

A declared IddCx hardware cursor is IRREVOCABLE for its OS target's life
(§8.6), and the sticky exclusion survives monitor REMOVE→ADD because each
client gets a STABLE target id — so once any desktop-mode session declared,
every later pure-capture session on that target streamed a cursor-less
desktop: DWM excluded the pointer, no channel forwarded it, no blend drew it
(the exact no-regression gap §8.6's per-session cap gate cannot see).

Driver: track every successful SetupHardwareCursor per target
(DECLARED_TARGETS — scoped to the WUDFHost's life, exactly the sticky
state's scope) and report it in a new AddReply::cursor_excluded tail field
(dual-size discipline, both skews degrade cleanly; no proto bump).

Host: the flag rides AddedMonitor → Monitor → WinCaptureTarget; a session
WITHOUT the cursor channel on a flagged target forces composite mode in the
IDD-push capturer — GDI poller + blend for the session's life, pinned on
(set_cursor_forward cannot clear it: with no client drawing, un-compositing
would erase the pointer entirely).

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

crates/pf-frame/src/dxgi.rs

@@ -32,6 +32,11 @@ pub struct WinCaptureTarget {
     /// duplicates the sealed frame channel's handles INTO (`idd_push::ChannelBroker`). `0` = unknown
     /// (a pre-v2 pairing can't occur — the version handshake is hard — so this only guards misuse).
     pub wudf_pid: u32,
+    /// The ADD reply flagged this target as carrying an IRREVOCABLE IddCx hardware-cursor declare
+    /// from an earlier session (remote-desktop-sweep §8.6): DWM excludes the pointer from its
+    /// frames forever, so a session WITHOUT the cursor channel must self-composite (the IDD-push
+    /// capturer's forced-composite gate) or the streamed desktop has no cursor at all.
+    pub cursor_excluded: bool,
 }
 
 /// The PyroWave (Windows) zero-copy sharing payload attached to a captured frame: the SECOND plane