- remove onBackPress interception (was swallowing back press to fake-confirm)
- '=' with no pending op no longer zeroes the display (AC + 2 + = was 0)
- AC no longer leaves stale fresh flag (first digit after AC appended to 0)
- leading zero replaced by first digit (00 + 2 was 002)
- operators auto-evaluate pending op (2+3x4 = 20, left-to-right)
- repeated = re-applies last operation (2+3=== -> 11)
- stale test updated to current list UI bindings