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/Settings/SettingsView.swift

@@ -25,6 +25,9 @@ struct SettingsView: View {
     @AppStorage(DefaultsKey.gamepadType) var gamepadType = 0
     @AppStorage(DefaultsKey.bitrateKbps) var bitrateKbps = 0
     @AppStorage(DefaultsKey.presenter) var presenter = "stage2"
+    #if os(macOS)
+    @AppStorage(DefaultsKey.vsync) var vsync = false
+    #endif
     @AppStorage(DefaultsKey.hdrEnabled) var hdrEnabled = true
     @AppStorage(DefaultsKey.enable444) var enable444 = true
     @AppStorage(DefaultsKey.libraryEnabled) var libraryEnabled = false
@@ -106,6 +109,7 @@ struct SettingsView: View {
             Form {
                 presenterSection
                 hdrSection
+                vsyncSection
                 windowSection
                 statisticsSection
             }