Update client data fetching and caching with tanstack query

[joshuagraber]

Context

Our client-side state has gotten complex enough in relationship with the server state that it now makes sense to add a proper querying and caching library.

Note: the current implementation is fine for the v2 launch, this is just something that is becoming necessary as the app gets more complex, so it's better to do it sooner than later.

Requirements

Tests

• Current client tests should pass.

Docs

• Remove references to pinia.
• Add links to Tanstack docs.

Open questions

• Evaluate whether Tanstack queries can be used with router loaders, or if we need to change that strategy. In some sense, trying to use loaders has turned out to be more headache than it's worth in our application.
  • Decision: we're going to remove the route loaders and use the queries directly.

[joshuagraber]

Adding hold label to wait until everything from the migration is in main here.