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/Package.swift

@@ -40,6 +40,8 @@ let package = Package(
         // its manifest breaks SwiftPM whole-graph validation on macOS, and only the
         // Punktfunk-tvOS target links it; the #if os(tvOS) import never compiles here.)
         .executableTarget(name: "PunktfunkClient", dependencies: ["PunktfunkKit"]),
-        .testTarget(name: "PunktfunkKitTests", dependencies: ["PunktfunkKit"]),
+        // PunktfunkCore is a direct dep too so the wire tests can name the C ABI's
+        // `PunktfunkInputEvent` / `PUNKTFUNK_INPUT_KIND_*` when asserting the gamepad byte layout.
+        .testTarget(name: "PunktfunkKitTests", dependencies: ["PunktfunkKit", "PunktfunkCore"]),
     ]
 )