fix: resolve all 16 failing tests across utility library

[stooit]

Summary

• calculator.ts: Throw Error("Division by zero") when divisor is 0 (was returning Infinity)
• string-utils.ts: Fix wordCount to handle consecutive spaces; implement truncate with word-boundary logic
• task-manager.ts: Implement remove, update, and sortBy methods
• date-utils.ts: Use Math.round instead of Math.floor for day calculation in formatRelative
• validator.ts: Allow TLDs longer than 4 chars in isEmail; allow port numbers in isUrl

Test Results

All 60 tests pass (previously 44 pass / 16 fail).

Assumptions

• truncate cuts at the last space before maxLength - 3 and appends "..." to stay within maxLength
• sortBy("priority") orders high > medium > low
• sortBy("createdAt") orders oldest first
• No test files were modified; no new dependencies added