Remove or replace StackBlitz demo

[tyler-reitz]

The StackBlitz demo linked from the docs has rotted and is no longer representative of the current library. Need to either update it to work with the current API or remove the link and replace with a working example.

Tracking this as part of broader doc cleanup.

[tyler-reitz]

Picking this back up as part of active maintenance. Here's where things stand:

• StackBlitz demo has rotted, needs dependency bumps to work with current API. Jeff owns the StackBlitz account so the call on whether to update or drop it is yours @jhuleatt.
• CodeSandbox created a working example (fix: update example to work with CodeSandbox and other cloud sandboxes #730) as a potential replacement, but it's brittle and may not be the right long-term home either.

@jhuleatt what's your preference: update the StackBlitz demo, switch to the CodeSandbox one from #730, or drop the live demo entirely and link to a code snippet in the docs?