feat(windows): IddCx hardware-cursor channel — remote-desktop sweep M2c

Brings the cursor channel to Windows hosts. The pf-vdisplay driver
declares an IddCx hardware cursor for sessions that negotiated
cursor-forward — DWM then EXCLUDES the pointer from the IDD frame and
delivers shape/position out-of-band, into the same CursorOverlay →
forwarder → wire → client pipeline the Linux portal path uses.

- pf-driver-proto v5 (additive, host floor stays 3): AddRequest's spare
  tail becomes hw_cursor (same size/offsets); IOCTL_SET_CURSOR_CHANNEL
  delivers a host-created CursorShm section (64-byte seqlock header +
  256² shape buffer, layout pinned + tested). No event crosses the
  boundary — the host polls at encode-tick pace.
- driver: wdk-iddcx grows the two cursor DDI wrappers; a per-monitor
  cursor worker (event wait → QueryHardwareCursor → seqlock publish)
  starts only when BOTH the ADD asked and the channel arrived, so a
  failed delivery leaves DWM compositing as today. Shape bytes ship raw
  (BGRA/masked + pitch); the host converts.
- host: the section rides the existing sealed-channel broker (least-
  privilege dup, remote reap on failure); IddPushCapturer::cursor()
  seqlock-reads → CursorOverlay (BGRA→RGBA, masked-color approximation,
  desktop→frame origin shift, per-shape conversion cache). New
  Capturer::cursor() trait hook — the encode loop prefers it over the
  frame-attached overlay because hardware-cursor moves produce NO new
  frame on a static desktop. hw_cursor survives the re-arrival resize
  (carried on the manager's Monitor).
- negotiation: cursor_forward grows the Windows arm (client cap ∧
  driver proto ≥ 5, probed once via the control device); SessionPlan
  carries cursor_forward → OutputFormat.hw_cursor.
- drive-by: wdk-probe's two pre-existing same-type casts (clippy) and
  pf-vdisplay's stale spike-test refs (crate::win_display moved to
  pf-win-display; tracing-subscriber was never a dep) repaired.

Verified: proto tests on Mac AND MSVC (15/15 incl. the CursorShm
layout pin); clippy -D warnings for proto/frame/capture/vdisplay/host
on Linux (.21) and native Windows (.173); the DRIVER workspace clippy
-D warnings green against the real WDK 10.0.26100 bindgen (DDI names,
enum variants and IDARG layouts all bind). On-box driver deploy +
on-glass validation follow.

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

crates/punktfunk-host/src/session_plan.rs

@@ -108,6 +108,10 @@ pub struct SessionPlan {
     /// Encoders whose fast path cannot blend (the Vulkan EFC RGB-direct source) stay on their
     /// blending path when this is set, so the pointer never silently vanishes from the stream.
     pub cursor_blend: bool,
+    /// The session negotiated the cursor-forward channel (M2/M2c): the client draws the pointer
+    /// locally, so `cursor_blend` is off AND (on Windows) the capturer sets the driver's
+    /// hardware cursor up via [`OutputFormat::hw_cursor`](pf_frame::OutputFormat).
+    pub cursor_forward: bool,
 }
 
 impl SessionPlan {
@@ -118,6 +122,7 @@ impl SessionPlan {
         chroma: crate::encode::ChromaFormat,
         codec: crate::encode::Codec,
         cursor_blend: bool,
+        cursor_forward: bool,
     ) -> Self {
         SessionPlan {
             capture: CaptureBackend::resolve(),
@@ -129,6 +134,7 @@ impl SessionPlan {
             codec,
             wire_chunk: None,
             cursor_blend,
+            cursor_forward,
         }
     }
 
@@ -171,6 +177,7 @@ impl SessionPlan {
         crate::capture::OutputFormat {
             gpu,
             hdr: self.hdr,
+            hw_cursor: self.cursor_forward,
             // 4:4:4 needs a full-chroma source: on Windows this keeps the capturer on RGB (not the
             // default NV12/P010 video-engine output) so NVENC can CSC to 4:4:4.
             chroma_444: self.chroma.is_444(),