fixes #3

Summary

• add optional task descriptions rendered with a small safe markdown parser
• support bold, italic, inline code, line breaks, and http/https/mailto links without using innerHTML
• persist descriptions through local storage and authenticated task APIs
• document markdown descriptions and cover parser/server sanitization behavior with tests

Validation

• npm test
• npm run lint
• node --check src/app.js
• node --check src/markdown.mjs
• node --check src/tasks.js
• node --check test/markdown.test.mjs
• node --check test/server.test.js
• npx prettier --check server.js src/markdown.mjs src/app.js src/tasks.js index.html styles.css test/markdown.test.mjs test/server.test.js README.md
• git diff --check
• local browser smoke on port 8020: rendered bold/italic/code/safe link and kept javascript: link as text