fix(android): launch games from the library

The library browser was browse-only — the A button (and a tap) did nothing.
Wire it to connect + boot straight into the selected title: thread a `launch`
id (the store-qualified library id `steam:<appid>` / `custom:<id>`) through
nativeConnect → NativeClient's Hello.launch (was hardcoded None), add a shared
connectToHost() the ConnectScreen and the library launcher both use, and have
LibraryScreen dial the host with launch=game.id on A / tap — with a launching
overlay + an "A Launch" hint. Verified: native compiles (cargo-ndk arm64),
app+kit Kotlin compiles (gradle, 3 ABIs).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

clients/android/kit/src/main/kotlin/io/unom/punktfunk/kit/NativeBridge.kt

@@ -51,6 +51,9 @@ object NativeBridge {
         /** Preferred video codec as a `quic::CODEC_*` bit (`0` = auto). Soft — the host falls back. */
         preferredCodec: Int,
         timeoutMs: Int,
+        /** Store-qualified library id (`steam:<appid>` / `custom:<id>`) to boot straight into a game,
+         *  or `null`/empty for a plain desktop connect. Rides the Hello as `launch`. */
+        launch: String?,
     ): Long
 
     /** 64-hex SHA-256 of the cert the host presented on [handle]; valid after a successful connect. */