Draft: feat(app): bootstrap initial Android app skeleton

Initial bootstrap MR for AlmanzRekt Android.

Included in this MR:

• add README.md and DEVELOPERS.md
• add architecture image for airgap and online modes
• add initial app source code
• add VERSIONING.md and CHANGELOG.md

Not ready for merge yet.

Planned before merge:

• perform clean clone test
• run fresh build locally
• test on two Android devices
• fix bugs and inconsistencies found during testing
• update docs if implementation changes