feat: add randomColor function to strings module

[JakobAyo]

Summary

Adds a new randomColor() function to the strings module that generates random hexadecimal color codes, implemented using Test-Driven Development (TDD).

Changes

• Added randomColor() function to src/strings.js:80-85

  • Generates random hex colors like #3a9f2b, #ff6b35
  • Zero dependencies, uses Math.random()

• Added comprehensive tests in tests/strings.test.js

  • Validates hex format, randomness
  • All tests passing ✓

• Updated README.md with usage example

TDD Implementation

1. ✓ Wrote failing test first
2. ✓ Verified failure
3. ✓ Implemented minimal code
4. ✓ All tests pass

Example Usage

import { randomColor } from './src/strings.js';
randomColor(); // "#3a9f2b"

🤖 Generated with https://claude.com/claude-code

[JakobAyo]

closes #8