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/Session/StreamCommands.swift

@@ -1,6 +1,11 @@
 // The app's "Stream" menu (macOS menu bar + iPad hardware-keyboard shortcuts). These live at
-// the Scene level so they keep working when the HUD overlay is hidden — in particular ⌘D
-// disconnect, which used to be reachable only via the HUD's button. The toggle just flips the
+// the Scene level so they keep working when the HUD overlay is hidden. The shortcuts are the
+// CROSS-CLIENT set every punktfunk client reserves — Ctrl+Alt+Shift+Q (release the captured
+// mouse) / +D (disconnect) / +S (stats) — and the menu is their discoverable surface on macOS
+// (the Linux client has its GTK Shortcuts window, Windows its start-of-stream banner). While
+// input is CAPTURED these key equivalents never reach the menu (the stream view swallows
+// keys); InputCapture's monitor detects the same combos there and performs the same actions —
+// the menu covers the released state and discoverability. The stats toggle just flips the
 // shared `hudEnabled` setting; ContentView reads the same @AppStorage and reacts.
 //
 // tvOS has no menu bar / hardware-keyboard command surface (disconnect there is the Siri
@@ -38,10 +43,19 @@ struct StreamCommands: Commands {
             Button(hudEnabled ? "Hide Statistics" : "Show Statistics") {
                 hudEnabled.toggle()
             }
-            .keyboardShortcut("s", modifiers: [.command, .shift])
+            .keyboardShortcut("s", modifiers: [.control, .option, .shift])
+            // Reaches the key window's stream view via NotificationCenter — capture is view
+            // state the Scene can't touch directly. (Captured, the combo is handled by
+            // InputCapture's monitor before menus see it; this item is the released-state
+            // path and the shortcut's menu-bar documentation.)
+            Button("Release Mouse") {
+                NotificationCenter.default.post(name: .punktfunkReleaseCapture, object: nil)
+            }
+            .keyboardShortcut("q", modifiers: [.control, .option, .shift])
+            .disabled(session?.isStreaming != true)
             Divider()
             Button("Disconnect") { session?.disconnect() }
-                .keyboardShortcut("d", modifiers: .command)
+                .keyboardShortcut("d", modifiers: [.control, .option, .shift])
                 .disabled(session?.isStreaming != true)
         }
     }

clients/apple/Sources/PunktfunkClient/Session/StreamHUDView.swift

@@ -64,10 +64,11 @@ struct StreamHUDView: View {
                     .foregroundStyle(.secondary)
             }
             // While captured the cursor is hidden+frozen, so the button is keyboard-only
-            // (⌘⎋ or Cmd+Tab release the cursor; released, it's clickable again).
+            // (⌃⌥⇧Q — the cross-client Ctrl+Alt+Shift+Q — or ⌘⎋/Cmd+Tab release the cursor;
+            // released, it's clickable again).
             #if os(macOS)
             Text(model.mouseCaptured
-                ? "⌘⎋ releases the mouse"
+                ? "⌃⌥⇧Q releases the mouse"
                 : "Click the stream to capture input")
                 .font(.geist(11, relativeTo: .caption2))
                 .foregroundStyle(.secondary)
@@ -87,10 +88,16 @@ struct StreamHUDView: View {
                 .font(.geist(12, relativeTo: .caption))
                 .foregroundStyle(.secondary)
             #else
-            // ⌘D lives on the app's Stream menu (so it still works when the HUD is hidden);
-            // this button is the in-overlay, click-to-disconnect affordance.
-            Button("Disconnect (⌘D)") { model.disconnect() }
+            // ⌃⌥⇧D lives on the app's Stream menu (so it still works when the HUD is hidden)
+            // and in InputCapture's monitor while captured; this button is the in-overlay,
+            // click-to-disconnect affordance.
+            #if os(macOS)
+            Button("Disconnect (⌃⌥⇧D)") { model.disconnect() }
                 .font(.geist(12, relativeTo: .caption))
+            #else
+            Button("Disconnect") { model.disconnect() }
+                .font(.geist(12, relativeTo: .caption))
+            #endif
             #endif
         }
         .padding(10)