feat(apple/ios): pen P4 — Apple Pencil (Pro) capture onto the stylus plane

The flagship leg of design/pen-tablet-input.md §7: against a HOST_CAP_PEN host
the Pencil splits out of the finger path (independent of touch-input mode) into
PencilStream — state-full samples with force→pressure, altitude→polar tilt,
azimuth (+90° to the wire's north-clockwise convention), Pencil Pro rollAngle→
barrel roll (17.5+), coalesced touches batched ≤8/send for full 240Hz fidelity,
and Pencil hover (zOffset>0 distinguishes it from trackpad hover) as in-range
samples with distance. Squeeze holds barrel 1, double-tap clicks barrel 2 (the
Pencil has no hardware buttons/eraser — these are how host apps get those
affordances). Implements the ≤100ms heartbeat wire contract (80ms timer) so a
stationary held stroke survives the host's 200ms dead-client failsafe. Toward a
pen-less host nothing changes (Pencil stays a finger).

Also fixes hostSupportsCursor testing the STALE 0x04 bit — HOST_CAP_CURSOR
moved to 0x08 when TEXT_INPUT claimed 0x04; the old test would mistake a
text-input host (e.g. Windows) for a cursor grant and double-render the pointer.

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

clients/apple/Sources/PunktfunkKit/Connection/PunktfunkConnection.swift

@@ -387,8 +387,16 @@ public final class PunktfunkConnection {
 
     /// The host answered `HOST_CAP_CURSOR`: it stopped compositing the pointer and forwards
     /// shape/state on the cursor planes — the client MUST draw the cursor locally.
+    /// `0x08` — the bit moved when `HOST_CAP_TEXT_INPUT` claimed `0x04` on main; testing the
+    /// old bit would mistake a text-input-capable host (e.g. Windows) for a cursor grant.
     public var hostSupportsCursor: Bool {
-        hostCaps & 0x04 != 0
+        hostCaps & 0x08 != 0
+    }
+
+    /// The host injects full-fidelity stylus input (`HOST_CAP_PEN`) — the gate for splitting
+    /// Apple Pencil out of the touch path onto the pen plane (``sendPen(_:)``).
+    public var hostSupportsPen: Bool {
+        hostCaps & UInt8(PUNKTFUNK_HOST_CAP_PEN) != 0
     }
 
     /// One forwarded host-cursor shape (the cursor channel, ABI v11): straight-alpha RGBA,
@@ -1133,6 +1141,19 @@ public final class PunktfunkConnection {
         _ = punktfunk_connection_send_input(h, &ev)
     }
 
+    /// Send one stylus sample batch (≤ `PUNKTFUNK_PEN_BATCH_MAX`, oldest first) on the pen
+    /// plane. Gate on ``hostSupportsPen`` — the core refuses toward a host without the cap.
+    /// Thread-safe; silently dropped after close (input is lossy by design).
+    public func sendPen(_ samples: [PunktfunkPenSample]) {
+        guard !samples.isEmpty else { return }
+        abiLock.lock()
+        defer { abiLock.unlock() }
+        guard let h = handle, !closeRequested else { return }
+        samples.withUnsafeBufferPointer { buf in
+            _ = punktfunk_connection_send_pen(h, buf.baseAddress, UInt32(buf.count))
+        }
+    }
+
     /// Signal a **deliberate** user-initiated quit before ``close()``: the connection closes with
     /// `QUIT_CLOSE_CODE` (81) so the host tears the session down immediately instead of holding the
     /// keep-alive linger for a reconnect. Call only from an explicit "Disconnect" action — NOT from a