🧪 [test] Add tests for truncate utility in format.ts

[toreleon]

🧪 What: Added missing unit tests for the truncate string utility in src/tui/lib/format.ts.
📊 Coverage: Covered happy paths (strings shorter, exactly matching, and longer than the limit) and edge cases including empty strings, limits of 0 or 1, and negative limit boundaries.
✨ Result: Improved test coverage and reliability for string manipulation utilities, catching regressions before they occur.

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PR created automatically by Jules for task 3615145940251670221 started by @toreleon

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