few small recipe additions -> download button, copy button, loading state, confirm dialog

[abhishekmamdapure]

saw the note in #74 about opening an issue before sending a PR
for anything new, so here goes.

I put together four small additions to the Recipes page: a download
button, a copy-to-clipboard button, a loading/submit button, and a
confirm-before-delete dialog. Nothing new in CSS or JS actually each one is
just existing primitives (button, dialog, the built-in spinner) wired
up with attributes and APIs that are already used elsewhere in the
docs; the Clipboard API, the hidden attribute, and the same
commandfor/command dialog pattern from dialog.md. So the bundle size
doesn't move at all, it's purely additive documentation.

Thanks for building this, its already helping us a lot.

[knadh]

Please send a PR. Will check.