RackDroid 0.1.1

Android 10+ support

Lowers minSdk from 33 to 29 (Android 10), fixing an install failure
reported in #2 ("problem analysing the package" — the app's minSdk 33
floor was unreachable on the reporter's device).

• Added a backtrace() shim (native/compat/execinfo.h) so the native engine
  no longer needs bionic's API-33-only <execinfo.h>.
• Fixed several API 30/31/33 calls (immersive mode, window insets,
  cross-window blur, typed getParcelableExtra) that would have crashed on
  Android 10-12 even after a successful install.
• Bluetooth LE MIDI scanning now works on Android 10-11 too (added the
  legacy permission fallback the newer BLUETOOTH_SCAN/CONNECT don't cover).

Signed with the project's public dev keystore (update-continuity for
existing sideload installs, not the Play production key).