create minimal app we can use to deploy interactive versions of mesa models to the sandbox server

[rlskoeser]

Solara can be deployed with Flask; see self-hosting Solara apps ; and a single solara app can be embedded as one part of a flask app using flask blueprints - so it seems like we ought to be able to create a simple flask app that provides a way to serve out multiple Mesa projects. I'm imagining a super-simple landing page with links to each simulation, and then use the existing solara app for each of our simulations that support it.

We'll also need a playbook for deploying the flask app to the sandbox; I'll track that under a separate task.

[rlskoeser]

solara app is running on the sandbox server; new deploy script reviewed and OKed.

some issues still to be resolved with the app itself, but those can be tracked separately