fix(apple): capture the PS/Home button + fullscreen only while streaming

Two issues from live Mac testing, plus a requested fullscreen option:

- PS button: the Home/PS button (→ guide; the host maps it to the DualSense PS bit)
  does not reliably fire GCExtendedGamepad.valueChangedHandler on macOS, so its presses
  were dropped. Add a dedicated buttonHome.pressedChangedHandler that re-syncs. The host
  already maps BTN_GUIDE→PS, so this is the missing client half.
- Fullscreen: a macOS FullscreenController (NSViewRepresentable) takes the window
  fullscreen while a session is up (incl. the trust prompt over the blurred stream) and
  restores it on the host list — so only the stream is fullscreen, not the picker. New
  `fullscreenWhileStreaming` setting (default on) + a Settings "Window" toggle.

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

clients/apple/Sources/PunktfunkKit/DefaultsKeys.swift

@@ -24,4 +24,6 @@ public enum DefaultsKey {
     public static let cursorMode = "punktfunk.cursorMode"
     /// Experimental: show the host's game library (browsed over the management API). Off by default.
     public static let libraryEnabled = "punktfunk.libraryEnabled"
+    /// macOS: take the window fullscreen while streaming and restore it on the host list. On by default.
+    public static let fullscreenWhileStreaming = "punktfunk.fullscreenWhileStreaming"
 }

clients/apple/Sources/PunktfunkKit/GamepadCapture.swift

@@ -169,6 +169,15 @@ public final class GamepadCapture {
         ext.valueChangedHandler = { [weak self] g, _ in
             MainActor.assumeIsolated { self?.sync(g) }
         }
+        // The Home/PS button (→ guide; the host maps it to the DualSense PS / Xbox guide bit) does
+        // NOT reliably fire the gamepad's valueChangedHandler on macOS, so its presses were dropped.
+        // A dedicated handler re-syncs on every Home transition.
+        ext.buttonHome?.pressedChangedHandler = { [weak self] _, _, _ in
+            MainActor.assumeIsolated {
+                guard let self, let g = self.bound?.extendedGamepad else { return }
+                self.sync(g)
+            }
+        }
         // Wake the host pad immediately (pads are created lazily from the first event;
         // a DualSense's UHID handshake + initial lightbar write only start then).
         connection.send(.gamepadAxis(GamepadWire.axisLSX, value: 0, pad: 0))