docs: update CONTRIBUTING for Vite and current npm scripts

[anth0nycodes]

What changes are introduced?

• npm run test:jest → npm run test (there is no test:jest script)
• npm run watch + opening ./docs/index.html → npm run dev and open the URL Vite prints
• Removed the mention of the docs folder, which no longer exists; the demo lives only in examples
• npm run build:demo is now just a check that the demo builds. Dropped "commit the file changes in the docs folder", since the build goes to dist/, which is gitignored
• Moved the lint and test step before the commit step, so contributors check their work before committing
• Removed the trailing ; from the commands and changed "Github" to "GitHub"