fix: implement missing utilities and fix edge-case bugs

[stooit]

Summary

Fixes all 16 previously failing tests across the utility library. The full suite now passes (60 pass / 0 fail). No test files were modified and no dependencies were added.

Changes

File	Fix
src/calculator.ts	divide now throws on division by zero
src/string-utils.ts	Implemented truncate (word-boundary, "..." counts toward maxLength, unchanged when str.length <= maxLength); fixed wordCount for consecutive spaces
src/task-manager.ts	Added remove, update, and sortBy (priority high > medium > low; createdAt oldest-first)
src/date-utils.ts	Fixed off-by-one in formatRelative at the hour/day boundary
src/validator.ts	isEmail accepts long TLDs (e.g. user@example.museum); isUrl accepts ports (e.g. http://localhost:3000)

Stale // BUG: JSDoc comments describing the now-fixed defects were removed to avoid misleading future readers.

Testing

bun test → 60 pass, 0 fail, 70 expect() calls.

Assumptions

• truncate behaviour for maxLength < 4 is not exercised by any test and was left as-is rather than over-engineering an uncovered edge case.
• Fixes were scoped strictly to what the tests require; no unrelated refactoring.

Verification

• Implementation delegated to the code agent, independently verified via bun test.
• Diff reviewed by the review agent — no correctness blockers.