fix: resolve all failing tests across utility library

[stooit]

Summary

• calculator.ts: Throw error on division by zero instead of returning Infinity
• string-utils.ts: Fix wordCount to handle multiple consecutive spaces; implement truncate with word-boundary logic
• task-manager.ts: Implement remove, update, and sortBy methods
• date-utils.ts: Use Math.round for days calculation so 36 hours displays as "2 days ago"
• validator.ts: Allow longer TLDs (e.g. .museum) in email validation; support port numbers in URL validation

Testing

All 60 tests pass (bun test). No test files were modified.

Assumptions

• truncate uses word-boundary truncation: if the string exceeds maxLength, it truncates to the last space that fits within maxLength - 3 and appends "...". If no word boundary fits, it hard-truncates at maxLength - 3.
• sortBy("priority") orders high > medium > low (descending severity).
• sortBy("createdAt") orders oldest first (ascending).