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>

crates/punktfunk-core/src/lib.rs

@@ -102,7 +102,7 @@ pub use stats::Stats;
 /// v10: added `punktfunk_connection_clock_offset_now_ns` — the LIVE (mid-stream re-synced)
 /// clock offset ongoing latency math must use; the connect-time getter stays frozen by
 /// contract. Additive, client-local — no wire change, so [`WIRE_VERSION`] is unchanged.
-pub const ABI_VERSION: u32 = 10;
+pub const ABI_VERSION: u32 = 11;
 
 /// The punktfunk/1 **wire** version — what `Hello`/`Welcome` carry and hosts equality-check.
 /// Deliberately its own constant: [`ABI_VERSION`] tracks the embeddable **C surface**