fix: repair 16 failing tests across utility library

[stooit]

Summary

Fixes all 16 failing tests across the TypeScript utility library. 60/60 tests now pass (was 44 pass / 16 fail). No test files modified, no dependencies added.

Changes by file

src/calculator.ts — divide throws Error("Division by zero") when the divisor is 0 instead of returning Infinity. The b === 0 guard also covers -0.

src/string-utils.ts

• wordCount splits on /\s+/ against the trimmed string, so consecutive spaces/tabs/newlines collapse correctly.
• truncate implemented: returns input unchanged when within maxLength; otherwise takes a maxLength - 3 budget, backs up to the last whitespace (regex /\s\S*$/, consistent with wordCount), and appends "...". Output is guaranteed <= maxLength, including when maxLength <= 3.

src/task-manager.ts — implemented three stubbed methods:

• remove — deletes by id, returns true/false.
• update — returns false for unknown ids; applies only explicitly-present fields (!== undefined) so omitted keys don't clobber existing values.
• sortBy — rank tables for priority (high→medium→low) and status, timestamp comparison for createdAt. Non-mutating (copies before sort); stable sort preserves insertion order on ties.

src/date-utils.ts — formatRelative rounds day deltas with Math.round(Math.abs(diffHours) / 24), so 36 hours reads as "2 days ago" and past/future directions are symmetric.

src/validator.ts

• isEmail — TLD cap widened from {2,4} to {2,} and domain modelled as explicit labels, so .museum and multi-level subdomains validate; labels can't start/end with a hyphen.
• isUrl — dropped the port === "" restriction (it wrongly rejected http://localhost:3000); the http/https protocol allow-list still enforces the intended restriction.

Verification

• bun test → 60 pass, 0 fail (70 assertions, 5 files)
• tsc --noEmit → clean
• Reviewed by the review subagent (verdict: no blockers). Two consistency Warnings it raised — formatRelative future-direction asymmetry and truncate whitespace handling — were fixed in the second commit.

Assumptions

• sortBy("status") ordering (pending→in_progress→completed) is not covered by tests; chose the natural lifecycle order.
• update cannot clear a field to undefined (an absent key and an explicit undefined are indistinguishable) — only matters if clearing is ever required.

Notes for follow-up (out of scope, not blocking)

• isEmail/isUrl are syntactic format checks, not security boundaries — isUrl accepts any http(s) host and should not be relied on as an SSRF control.
• The newly-fixed future-direction and tab/newline cases would be worth adding as regression tests.