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/PunktfunkClient/PunktfunkClientApp.swift

@@ -43,8 +43,9 @@ struct PunktfunkClientApp: App {
             // form row labels; views that pick an explicit size/weight use `.geist(…)` directly.
             .font(.geist(17, relativeTo: .body))
         }
-        // The Stream menu (Disconnect ⌘D, Show/Hide Statistics ⌘⇧S) — a real menu bar on
-        // macOS, hardware-keyboard shortcuts on iPad. tvOS has neither.
+        // The Stream menu (Release Mouse ⌃⌥⇧Q, Disconnect ⌃⌥⇧D, Show/Hide Statistics ⌃⌥⇧S —
+        // the cross-client Ctrl+Alt+Shift set) — a real menu bar on macOS, hardware-keyboard
+        // shortcuts on iPad. tvOS has neither.
         #if !os(tvOS)
         .commands { StreamCommands() }
         #endif