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/PunktfunkClient/Settings/SettingsView+Support.swift

@@ -133,8 +133,10 @@ extension SettingsView {
                 .foregroundStyle(.secondary)
             }
             Spacer()
-            if gamepads.active?.id == controller.id {
-                Text("In use")
+            // Every forwarded controller is surfaced (not just the primary `active`) with its
+            // wire pad index as a player number — a pin forwards only one, Automatic forwards all.
+            if let pad = gamepads.padIndex(for: controller) {
+                Text("Player \(pad + 1)")
                     .font(.geist(11, .semibold, relativeTo: .caption2))
                     .padding(.horizontal, 8)
                     .padding(.vertical, 3)