mpckit-site/pull-releases/003-mpckit-casing

Use the name MPCkit

What changed

• public/index.html: the app is called MPCkit in the page title, link previews, wordmark, heading, text and image descriptions.
• README.md, nginx/mpckit.monoexp.com.conf: the same in their text.

Notes

• Lowercase stays where it's a name on disk or online: the site's address, repository names and links, and the build files (mpckit.exe, mpckit.app, mpckit).
• The screenshots still show "mpckit" in the window title, as the app does today.

Testing

• Served public/ locally and checked desktop and mobile screenshots.