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/PunktfunkKit/Licenses.swift

@@ -0,0 +1,36 @@
+import Foundation
+
+/// Open-source license / attribution text bundled with PunktfunkKit (see `Resources/`).
+///
+/// Exposed from the kit so the app shell can show an Acknowledgements screen. The text files are
+/// bundled as SwiftPM resources and read via `Bundle.module`, which works both for `swift build`
+/// and for the Xcode app (it links the PunktfunkKit product, so the resource bundle rides along).
+public enum Licenses {
+    private static func resource(_ name: String) -> String {
+        guard let url = Bundle.module.url(forResource: name, withExtension: "txt"),
+            let text = try? String(contentsOf: url, encoding: .utf8)
+        else { return "" }
+        return text
+    }
+
+    /// punktfunk's own license — MIT OR Apache-2.0, at your option.
+    public static var appLicense: String {
+        let mit = resource("LICENSE-MIT")
+        let apache = resource("LICENSE-APACHE")
+        if mit.isEmpty && apache.isEmpty {
+            return "punktfunk is licensed under MIT OR Apache-2.0, at your option."
+        }
+        return "punktfunk is licensed under MIT OR Apache-2.0, at your option.\n\n"
+            + "================================ MIT ================================\n\n"
+            + mit
+            + "\n\n============================== Apache-2.0 ==============================\n\n"
+            + apache
+    }
+
+    /// Third-party software notices for the linked Rust crates (generated by
+    /// `scripts/gen-third-party-notices.sh`).
+    public static var thirdPartyNotices: String {
+        let text = resource("THIRD-PARTY-NOTICES")
+        return text.isEmpty ? "Third-party notices unavailable." : text
+    }
+}