Add markdown task descriptions

[Jorel97]

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

[codebounty-dev-bot]

⚠️ Attention Sponsor: This PR was submitted by @Jorel97 who has not applied for this bounty (#3). Please verify if you want to consider this contribution.

👋 Hey @Jorel97: This issue has a bounty on CodeBounty! To be eligible for the reward, please sign up on CodeBounty and apply for this bounty. If you apply, your PR will be automatically associated with your application.

[Jorel97]

Hi CodeBounty/sponsor team, I logged in to CodeBounty as @Jorel97 and opened the bounty/repository views for #3. The bounty currently appears to require approval / does not expose a developer Apply button from my account.

This PR was submitted for the $75 bounty on #3. Could you please confirm whether maintainer approval is required before applications can be submitted, and whether this PR can be associated with my application once the bounty is open?