docs: add harper.js Chrome extension intro and example

[Hashim1999164]

Issues

Fixes #3628

Description

Adds a minimal MV3 Chrome extension example under packages/harper.js/examples/chrome-extension-simple that loads local harper.js, shows the package version, and runs a one-line lint.

Documents extension-specific constraints (MV3 CSP, popup vs service worker, prefer local dist over unpkg) at /docs/harperjs/chrome-extension.

Wires the page into the docs sidebar and links it from the harper.js introduction and CDN pages. Points readers at packages/harper.js/examples.

Demo

N/A (documentation and example scaffolding)

How Has This Been Tested?

• Confirmed sidebar wiring in packages/web/vite.config.ts
• Skimmed /docs/harperjs/chrome-extension for accuracy and links
• Reviewed the example package layout

AI Disclosure

• I used an AI agent interactively.
• I am a human and didn't use any AI.
• I used LLM features of my editor, but not an agent.
• I am an agent or I got an agent to do the work autonomously.

If Your PR Implements or Enhances a Linter

• I made up the sentences in the unit tests.
• The sentences in the unit tests were generated by an AI.
• I'm using examples from the bug report / feature request.
• I collected real-world sentences for the unit tests.

Checklist

• I have performed a self-review of my own code
• I have added tests to cover my changes
• I have considered splitting this into smaller pull requests.

[hippietrail]

Thanks for this, it looks very promising. I see that you did include an AI disclaimer, but could you please use our GitHub PR template, it has a couple more questions.

[Hashim1999164]

Thanks for the note. I've updated the PR description to follow the GitHub PR template (issues, description, demo, testing, AI disclosure, and checklist).