- Expanded calc_test.go with additional cases for decimal point, backspace, sign change, mod, div0, multi-step ops, negatives, format, is-integer with entry, etc. (calc coverage to ~86%)
- New ui_test.go: unit tests for App (New, Update key sequences for digits/ops/MOD/HEX entry/base cycle/CERR/clears/flashes/pressed state, View contains checks). ui coverage ~82%
- New version_test.go: 100% for String()
- All tests pass (go test ./...); total project coverage ~81%
- Complements the HEX entry and UI polish work.
- Uses table-friendly and direct model testing suitable for the Bubble Tea spike.
