Rewrite chat in indigo-react

[matildepark]

• Starting with /lib/ folder
• Componentising the /lib/ folder without boundaries work

More intense version:

• Starting with skeleton.js
• Working down through the more top-level components, reorganising as you go

Single concern components, but not composable (not generic; very specific views) — might be worth re-evaluating component organisation

[matildepark]

On pause while we do prerequisite work for graph-store FE (links migration FE case).

[matildepark]

Still on pause — @liam-fitzgerald may start to take this over as a stretch goal this week until we have design mockups for the new user stories for group-centred use.

(Don't get too obsessed with the task, doing a refactor a bit at a time is okay.)