Remove AIDL and merge to single process

[powerje]

Summary

• Merge StellarService into the main app process (remove android:process=":stellar")
• Replace AIDL binding with local binding — MainWindow, Launcher, and all dialog classes get a direct StellarService reference
• Replace all three AIDL callback interfaces (IConnectionBinderCallback, IWindowCallback, ILauncherCallback) with plain Java interfaces
• Delete all 29 .aidl files and remove AIDL build feature
• Remove Parcelable boilerplate from 28 data classes
• Add GitHub Actions CI workflow
• Track prebuilt native .so libraries for CI builds

Test plan

• Build succeeds locally
• App installs and launches
• Single process confirmed (adb shell ps shows one process, no :stellar)
• Can connect to a MUD and interact
• CI build passes