fix: repair failing tests across utility library

[stooit]

Summary

Fixes all 16 previously failing tests across the TypeScript utility library. All 60 tests now pass (0 fail), with none of the 44 previously-passing tests broken. No test files were modified and no dependencies were added.

Changes

• src/calculator.ts — divide now throws on division by zero instead of returning Infinity.
• src/string-utils.ts — wordCount now handles consecutive whitespace correctly (splits on /\s+/ after trim); truncate implemented to cut at a word boundary with the ellipsis counting toward maxLength.
• src/task-manager.ts — implemented the previously-stubbed remove, update, and sortBy methods.
• src/date-utils.ts — fixed off-by-one in formatRelative (rounds instead of floors, so 36h → "2 days ago").
• src/validator.ts — isEmail now accepts long TLDs (e.g. .museum); isUrl now accepts an optional port (e.g. http://localhost:3000).
• Removed stale BUG: JSDoc comments that described the now-fixed behaviour.

Assumptions

• Interpreted each fix strictly against the behaviour the tests assert; left edge cases not covered by tests unchanged to avoid regressing passing tests (per "fix only what the tests require").
• divide throws a generic Error("Division by zero") — no specific error type was mandated by the tests.

Testing

bun test → 60 pass, 0 fail (70 expect() calls, 5 files).

Reviewed by the review subagent; no blocking issues found.