feat(apple): multi-controller support

Roll the pf-client-core slot pattern to the Apple client (Swift):

- GamepadManager tracks all connected GCControllers, assigning each a stable
  lowest-free wire pad index + concrete type, emitting GamepadArrival on
  connect and GamepadRemove on disconnect (index freed for reuse on re-plug).
- GamepadCapture binds every controller with per-controller Slot state
  (buttons/axes/fingers/motion), threading the pad index into flags on every
  event; GamepadWire/InputEvents carry the pad + the two new events.
- GamepadFeedback + RumbleRenderer go per-pad (rumbleByPad, slots[pad]),
  routing rumble/HID back to the correct controller by wire index.
- ContentView/Settings surface every forwarded controller.

pad 0 => flags 0, so single-controller wire is byte-identical. Cannot build
on the Linux dev box (no Swift toolchain / Apple frameworks); wire bytes
hand-checked against input.rs and GamepadWireTests extended for multi-pad.
CI apple.yml (swift build/test on macOS) is the compile gate.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/apple/Sources/PunktfunkKit/Gamepad/GamepadWire.swift

@@ -1,10 +1,14 @@
 // The gamepad wire contract shared by capture (GamepadCapture), feedback (GamepadFeedback),
-// and the tests — button bits, axis ids, and the touchpad/motion unit conversions.
+// and the tests — the pad count, button bits, axis ids, and the touchpad/motion unit conversions.
 
 import Foundation
 
 /// The gamepad wire contract (mirrors `punktfunk_core::input::gamepad`).
 public enum GamepadWire {
+    /// Gamepads addressable on the wire — the pad index rides the low byte of `flags` on every
+    /// per-pad event, 0...15 (`punktfunk_core::input::MAX_PADS`).
+    public static let maxPads: Int = 16
+
     public static let dpadUp: UInt32 = 0x0001
     public static let dpadDown: UInt32 = 0x0002
     public static let dpadLeft: UInt32 = 0x0004