feat(apple): cursor channel on the Mac client — ABI v11 + NSCursor rendering

The Mac client now exercises the full cursor channel against capable
hosts: desktop-mode sessions advertise CLIENT_CAP_CURSOR, the host
stops compositing the pointer, and StreamView draws the forwarded
shapes as the real NSCursor — plus the M3 host-driven model flip.

- ABI v11: punktfunk_connect_ex9 (adds client_caps; ex7/ex8 pass 0 —
  Android untouched), PunktfunkCursorShape/State + the two
  next_cursor_* poll fns (audio-style borrow contract), and
  PUNKTFUNK_CLIENT_CAP_CURSOR. Fixed in passing: the first insertion
  split next_host_timing's cfg/no_mangle attributes off the fn, which
  silently dropped the symbol from the header AND dylib — caught by
  the Swift build, reattached with its docs.
- PunktfunkConnection: clientCaps connect param, hostSupportsCursor,
  CursorShapeEvent/CursorStateEvent + nextCursorShape/nextCursorState
  (one cursor thread drains both planes; cursorLock joins the close()
  ladder).
- SessionModel: desktop-mode sessions (DefaultsKey.mouseMode) connect
  with the cursor cap on macOS.
- StreamView: shape cache (serial → NSCursor, straight-alpha RGBA via
  CGImage), resetCursorRects wears the HOST shape while the desktop
  model is engaged (hidden host pointer ⇒ invisible), latest-wins
  state pump, and the M3 auto-flip — edge-triggered on relative_hint,
  ⌃⌥⇧M sets an override latch cleared by the next host edge, leaving
  relative warps the pointer to the host position via the inverse
  letterbox mapping (CGWarpMouseCursorPosition, CursorCapture's
  coordinate convention).

Verified: swift build + full test suites green (xcframework rebuilt at
ABI v11, signed); core 218 tests + clippy -D warnings on Linux (.21).

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

clients/apple/Sources/PunktfunkClient/Session/SessionModel.swift

@@ -302,13 +302,26 @@ final class SessionModel: ObservableObject {
             if preferredCodec == PunktfunkConnection.codecPyroWave, MetalWaveletDecoder.supported {
                 videoCodecs |= PunktfunkConnection.codecPyroWave
             }
+            // Cursor channel (remote-desktop-sweep M2, macOS): sessions STARTING in the desktop
+            // mouse model advertise local cursor rendering — the host then stops compositing
+            // the pointer and forwards shape/state, which StreamView draws as the real
+            // NSCursor. Capture-mode sessions keep today's composited pointer.
+            #if os(macOS)
+            let clientCaps: UInt8 =
+                (MouseInputMode(
+                    rawValue: UserDefaults.standard.string(forKey: DefaultsKey.mouseMode) ?? "")
+                    ?? .capture) == .desktop ? 0x01 : 0
+            #else
+            let clientCaps: UInt8 = 0
+            #endif
             let result = Result { try PunktfunkConnection(
                 host: host.address, port: host.port,
                 width: width, height: height, refreshHz: hz,
                 pinSHA256: pin, identity: identity, compositor: compositor,
                 gamepad: gamepad, bitrateKbps: bitrateKbps, videoCaps: videoCaps,
                 audioChannels: audioChannels,
-                videoCodecs: videoCodecs, preferredCodec: preferredCodec, launchID: launchID,
+                videoCodecs: videoCodecs, preferredCodec: preferredCodec,
+                clientCaps: clientCaps, launchID: launchID,
                 // Delegated approval: the host holds this connect open until the operator approves
                 // it (~180 s) — outwait that window so a slow approval still lands here. Normal
                 // connects keep the snappy default.