feat(clients/apple): cross-client shortcuts + start banner, opt-in V-Sync, presenter rework

Align the macOS/iPad Stream menu on the cross-client Ctrl+Alt+Shift set
the Windows and Linux clients reserve — Release Mouse (⌃⌥⇧Q), Disconnect
(⌃⌥⇧D), HUD toggle (⌃⌥⇧S) — with ⌘⎋ kept as the macOS/iPad capture
toggle, and surface them on a 6-second banner at stream start.

Add an opt-in V-Sync present mode (punktfunk.vsync, default OFF =
lowest-latency immediate present; PUNKTFUNK_PRESENT_MODE overrides for
A/B), with the presenter reworked to a frame-arrival-triggered render
thread across Stage2Pipeline / MetalVideoPresenter / SessionPresenter,
plus the windowed title-bar safe-area handling.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

clients/apple/Sources/PunktfunkKit/Views/StreamViewIOS.swift

@@ -54,10 +54,15 @@ public struct StreamView: UIViewControllerRepresentable {
     private let decodeMeter: LatencyMeter?
     private let displayMeter: LatencyMeter?
 
+    /// `onDisconnectRequest` exists for call-site parity with the macOS StreamView (the
+    /// captured-state ⌃⌥⇧D combo is detected by the macOS NSEvent monitor only); on iOS a
+    /// hardware keyboard reaches Disconnect through the Stream menu's key equivalent instead,
+    /// so the parameter is accepted and unused here.
     public init(
         connection: PunktfunkConnection,
         captureEnabled: Bool = true,
         onCaptureChange: ((Bool) -> Void)? = nil,
+        onDisconnectRequest: (() -> Void)? = nil,
         onFrame: (@Sendable (AccessUnit) -> Void)? = nil,
         onSessionEnd: (@Sendable () -> Void)? = nil,
         endToEndMeter: LatencyMeter? = nil,