Summary

Fixes all 16 previously-failing tests across 5 utility modules. All 60 tests now pass (bun test), and tsc --noEmit is clean. No test files were modified and no dependencies were added — fixes are minimal and scoped to what the tests require.

Changes

• src/calculator.ts — divide now throws "Division by zero" when the divisor is 0 (was returning Infinity).
• src/string-utils.ts — wordCount trims and splits on /\s+/ so consecutive spaces no longer count as words; truncate implemented (returns unchanged within limit, truncates at word boundary, ellipsis counts toward maxLength, handles strings shorter than the ellipsis).
• src/task-manager.ts — completed the missing/incomplete remove, update, and sortBy methods (priority high→medium→low; createdAt oldest-first; unknown IDs return false).
• src/date-utils.ts — formatRelative uses Math.round instead of Math.floor for the day count, fixing the off-by-one (36 hours → "2 days ago").
• src/validator.ts — isEmail accepts long TLDs and subdomains (e.g. user@example.museum); isUrl accepts URLs with a port (e.g. http://localhost:3000).

Verification

• bun test: 60 pass / 0 fail
• bunx tsc --noEmit: clean
• Reviewed by review subagent: no blockers.

Notes / Assumptions

• Per the task constraint "fix only what the tests require", a few pre-existing untested edge cases were left as-is: truncate with maxLength <= 0, the 23h59m cosmetic boundary in formatRelative, and alphabetical ordering for sortBy("status"). None are exercised by the suite and none are regressions.