feat(sdk): add Swift and Kotlin mobile client foundations with push token proto

Swift SDK: Swift Package wrapping libquicproquo_ffi with QpqClient class
(connect, login, send, receive, disconnect) for iOS 15+ / macOS 13+.

Kotlin SDK: JNI bridge to libquicproquo_ffi with QpqClient class for
Android (aarch64, armv7) and JVM, Gradle build configuration.

Adds RegisterPushToken RPC (method ID 710) to device.proto for
APNs/FCM/WebPush device push token registration.

sdks/swift/Package.swift

@@ -0,0 +1,32 @@
+// swift-tools-version: 5.9
+// QuicProQuo Swift SDK — wraps libquicproquo_ffi for iOS/macOS.
+
+import PackageDescription
+
+let package = Package(
+    name: "QuicProQuo",
+    platforms: [
+        .iOS(.v15),
+        .macOS(.v13),
+    ],
+    products: [
+        .library(name: "QuicProQuo", targets: ["QuicProQuo"]),
+    ],
+    targets: [
+        .systemLibrary(
+            name: "CQuicProQuo",
+            pkgConfig: nil,
+            providers: []
+        ),
+        .target(
+            name: "QuicProQuo",
+            dependencies: ["CQuicProQuo"],
+            path: "Sources/QuicProQuo"
+        ),
+        .testTarget(
+            name: "QuicProQuoTests",
+            dependencies: ["QuicProQuo"],
+            path: "Tests/QuicProQuoTests"
+        ),
+    ]
+)