[Borisserz]

Summary

Fixes #417. TokenFormatter.percent and costCompact chose their precision from the raw value and rounded afterwards. When rounding crossed a boundary, the output contradicted the choice: 79.96 became 80.0%, 99.96 became $100.0, and 9_999.6 became $10000 instead of $10.0K.

Both functions now format with the bucket's precision first and pick the bucket from the formatted value. Output for every non-boundary value is unchanged: the existing testFormatterEdges assertions still pass as-is.

Type of change

• Bug fix
• New feature
• Refactor / cleanup
• Documentation
• Other:

UI changes

Before	After
Menu bar 5h 80.0% next to 7d 88%; recap ▲13.0%; cost $100.0 / $10000	5h 80%, ▲13%, $100 / $10.0K

Validation

• New LocalUsageCacheTests.testFormatterRoundingBoundaries with pairs just above and just below each boundary (79.96/79.94, 99.96/99.94, 9_999.6/9_999.4, plus 99.97 and 0.04). On unfixed main it fails with 5 failures. With the fix, all pass.
• Full swift test: 1385 tests, 0 failures (17 skipped, as on main).
• Class sweep: L.difficultyValue has the same shape, but snapDifficulty snaps every slider value to 2 significant digits, so no input can round across its boundaries. Left unchanged and noted in the defect log.
• Added a defect-log entry under display/UI.

Checklist

• swift build and swift test pass locally
• PR title and description are written in English
• UI changes are described above (before/after — images optional)
• No copyrighted assets, secrets, or private tooling references are committed (see CONTRIBUTING)
• Tests were added or updated for this change