feat(apple): client-selectable compositor in the macOS client

Adopts punktfunk_connect_ex from the compositor-selection batch: a Compositor enum on
PunktfunkConnection (auto/kwin/wlroots/mutter/gamescope, with the host's name aliases
for env parsing), a "Host compositor" picker in Settings (default Automatic — a
concrete choice is honored only if that backend is available host-side), and
PUNKTFUNK_COMPOSITOR / PUNKTFUNK_REMOTE_COMPOSITOR pass-throughs for the autoconnect
dev hook and the remote first-light test. The wire change is backward-compatible
(optional trailing byte), so no behavior changes at the default.

Validated live against the box: host with no compositor env (auto-detect = KWin)
logged "honoring client compositor request compositor=gamescope" and streamed 60/60
decoded frames from the spawned gamescope.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/SettingsView.swift

@@ -1,13 +1,16 @@
-// App settings (⌘,): the stream mode. The host creates a native virtual output at
-// exactly this size/refresh — there is no scaling anywhere in the pipeline.
+// App settings (⌘,): the stream mode + the host compositor. The host creates a native
+// virtual output at exactly this size/refresh — there is no scaling anywhere in the
+// pipeline.
 
 import AppKit
+import PunktfunkKit
 import SwiftUI
 
 struct SettingsView: View {
     @AppStorage("punktfunk.width") private var width = 1920
     @AppStorage("punktfunk.height") private var height = 1080
     @AppStorage("punktfunk.hz") private var hz = 60
+    @AppStorage("punktfunk.compositor") private var compositor = 0
 
     var body: some View {
         Form {
@@ -30,6 +33,23 @@ struct SettingsView: View {
                     .font(.caption)
                     .foregroundStyle(.secondary)
             }
+            Section {
+                Picker("Compositor", selection: $compositor) {
+                    Text("Automatic").tag(0)
+                    Text("KWin (KDE Plasma)").tag(1)
+                    Text("wlroots (Sway / Hyprland)").tag(2)
+                    Text("Mutter (GNOME)").tag(3)
+                    Text("gamescope").tag(4)
+                }
+            } header: {
+                Text("Host compositor")
+            } footer: {
+                Text("Which compositor drives the virtual output on the host. A specific "
+                    + "choice is honored only if that backend is available there — "
+                    + "otherwise the host falls back to auto-detection.")
+                    .font(.caption)
+                    .foregroundStyle(.secondary)
+            }
         }
         .formStyle(.grouped)
         .frame(width: 380)