docs: correct Android behavior description for externalCallSystem

On Android the mode currently behaves like automatic, not manual. The
Android session configure and speakerphone paths still run, since the
activation flag only exists on iOS. This is the intended interim
behavior: a cross-platform app sets the mode once and Android keeps
normal session management until Telecom integration lands.

Author: hiroshihorie

lib/src/audio/audio_session.dart

@@ -37,9 +37,11 @@ enum AudioSessionManagementMode {
   /// with `AudioManager.setEngineAvailability` so the engine only runs inside
   /// CallKit's `didActivate`/`didDeactivate` window.
   ///
-  /// On Android this currently behaves like [manual]. When Telecom
-  /// (`androidx.core.telecom`) integration lands, this mode will also stand
-  /// down LiveKit's audio-focus and routing management, which the Telecom
+  /// On Android this currently behaves like [automatic], so a cross-platform
+  /// app can set this mode once at startup: iOS gets the CallKit contract and
+  /// Android keeps LiveKit's normal session management. When Telecom
+  /// (`androidx.core.telecom`) integration lands, this mode will stand down
+  /// LiveKit's audio-focus and routing management, which the Telecom
   /// framework owns for registered calls.
   externalCallSystem,
 }