feat(clients): in-app OSS / third-party-license screens

Surface THIRD-PARTY-NOTICES.txt in every GUI client (the desktop packages already
ship it as a file; this adds the on-glass screen):

- Linux: Preferences -> About -> Third-party licenses (adw::AboutDialog with the app
  license + Legal sections; include_str! the root notices).
- Apple: macOS About tab / iOS+tvOS Acknowledgements link; notices bundled as
  PunktfunkKit SPM resources, read via Bundle.module (the Xcode app links the SPM
  product, so they ride along - no .pbxproj edit).
- Android: Settings -> About -> Open-source licenses (reads the bundled asset).
- (Windows landed earlier in d1d2ca2: Settings -> About -> Third-party licenses.)

gen-third-party-notices.sh now copies the generated file into the Apple Resources/
and Android assets/ trees so the in-tree copies never drift.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/apple/Sources/PunktfunkClient/AcknowledgementsView.swift

@@ -0,0 +1,60 @@
+import PunktfunkKit
+import SwiftUI
+
+/// Open-source acknowledgements: punktfunk's own license (MIT OR Apache-2.0) followed by the
+/// third-party software notices. Used as a pushed view on iOS/tvOS and a preferences tab on macOS.
+struct AcknowledgementsView: View {
+    private var version: String? {
+        Bundle.main.infoDictionary?["CFBundleShortVersionString"] as? String
+    }
+
+    var body: some View {
+        ScrollView {
+            VStack(alignment: .leading, spacing: 18) {
+                Text("punktfunk")
+                    .font(.title2).bold()
+                if let version {
+                    Text("Version \(version)")
+                        .font(.caption)
+                        .foregroundStyle(.secondary)
+                }
+                Text(Licenses.appLicense)
+                    .font(.caption.monospaced())
+                    .modifier(SelectableText())
+
+                Divider()
+
+                Text("Third-party software")
+                    .font(.headline)
+                Text(
+                    "punktfunk uses the open-source components below, each under its own license. "
+                        + "On some platforms FFmpeg is additionally bundled under the LGPL v2.1+ "
+                        + "(dynamically linked, replaceable)."
+                )
+                .font(.caption)
+                .foregroundStyle(.secondary)
+                Text(Licenses.thirdPartyNotices)
+                    .font(.caption2.monospaced())
+                    .modifier(SelectableText())
+            }
+            .frame(maxWidth: 900, alignment: .leading)
+            .frame(maxWidth: .infinity, alignment: .leading)
+            .padding()
+            #if os(tvOS)
+                .padding(40)
+            #endif
+        }
+        .navigationTitle("Acknowledgements")
+    }
+}
+
+/// `textSelection(.enabled)` is unavailable on tvOS, so apply it only where it exists.
+private struct SelectableText: ViewModifier {
+    func body(content: Content) -> some View {
+        #if os(tvOS)
+            content
+        #else
+            content.textSelection(.enabled)
+        #endif
+    }
+}

clients/apple/Sources/PunktfunkClient/SettingsView.swift

@@ -98,6 +98,9 @@ struct SettingsView: View {
             }
             .formStyle(.grouped)
             .tabItem { Label("Advanced", systemImage: "slider.horizontal.3") }
+
+            AcknowledgementsView()
+                .tabItem { Label("About", systemImage: "info.circle") }
         }
         .frame(width: 480, height: 460)
     }
@@ -115,6 +118,9 @@ struct SettingsView: View {
             statisticsSection
             experimentalSection
             controllersSection
+            Section {
+                NavigationLink("Acknowledgements") { AcknowledgementsView() }
+            }
         }
         .formStyle(.grouped)
         .onAppear {
@@ -217,6 +223,8 @@ struct SettingsView: View {
                     .foregroundStyle(.secondary)
                     .multilineTextAlignment(.center)
                     .padding(.top, 8)
+                NavigationLink("Acknowledgements") { AcknowledgementsView() }
+                    .padding(.top, 8)
             }
             .frame(maxWidth: 1000)
             .frame(maxWidth: .infinity)