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/linux/src/ui_settings.rs

@@ -19,6 +19,49 @@ const REFRESH: &[u32] = &[0, 30, 60, 90, 120, 144, 165, 240];
 const GAMEPADS: &[&str] = &["auto", "xbox360", "dualsense", "xboxone", "dualshock4"];
 const COMPOSITORS: &[&str] = &["auto", "kwin", "wlroots", "mutter", "gamescope"];
 
+/// punktfunk's own license (MIT OR Apache-2.0), shown on the About dialog's Legal page.
+const APP_LICENSE: &str = concat!(
+    "punktfunk is licensed under MIT OR Apache-2.0, at your option.\n\n",
+    "================================ MIT ================================\n\n",
+    include_str!("../../../LICENSE-MIT"),
+    "\n\n=============================== Apache-2.0 ===============================\n\n",
+    include_str!("../../../LICENSE-APACHE"),
+);
+/// Third-party software notices for the linked Rust crates (generated by
+/// scripts/gen-third-party-notices.sh; shown as a Legal section in the About dialog).
+const THIRD_PARTY_NOTICES: &str = include_str!("../../../THIRD-PARTY-NOTICES.txt");
+
+/// Show the About dialog (app license + the third-party-software Legal section).
+fn show_about(parent: &impl IsA<gtk::Widget>) {
+    let about = adw::AboutDialog::builder()
+        .application_name("punktfunk")
+        .developer_name("unom")
+        .version(env!("CARGO_PKG_VERSION"))
+        .website("https://git.unom.io/unom/punktfunk")
+        .license_type(gtk::License::Custom)
+        .license(APP_LICENSE)
+        .build();
+    // The native (FFmpeg/GTK/PipeWire/SDL3) components are dynamically linked under their own
+    // (LGPL/Zlib/MIT) licenses; the Rust crate notices are the substantive attribution set.
+    about.add_legal_section(
+        "Third-party software (Rust crates)",
+        None,
+        gtk::License::Custom,
+        Some(THIRD_PARTY_NOTICES),
+    );
+    about.add_legal_section(
+        "Third-party software (system libraries)",
+        None,
+        gtk::License::Custom,
+        Some(
+            "This application dynamically links system libraries under their own licenses, \
+             including FFmpeg (LGPL v2.1+), GTK 4 and libadwaita (LGPL v2.1+), PipeWire (MIT), \
+             and SDL 3 (Zlib). Their full license texts are available from each project.",
+        ),
+    );
+    about.present(Some(parent));
+}
+
 pub fn show(
     parent: &impl IsA<gtk::Widget>,
     settings: Rc<RefCell<Settings>>,
@@ -156,9 +199,23 @@ pub fn show(
         .build();
     audio.add(&mic_row);
 
+    let about = adw::PreferencesGroup::builder().title("About").build();
+    let licenses_row = adw::ActionRow::builder()
+        .title("Third-party licenses")
+        .subtitle("Open-source software used by punktfunk")
+        .activatable(true)
+        .build();
+    licenses_row.add_suffix(&gtk::Image::from_icon_name("go-next-symbolic"));
+    {
+        let about_parent: gtk::Widget = parent.clone().upcast();
+        licenses_row.connect_activated(move |_| show_about(&about_parent));
+    }
+    about.add(&licenses_row);
+
     page.add(&stream);
     page.add(&input);
     page.add(&audio);
+    page.add(&about);
 
     // Seed from the current settings.
     {