Add workflow/chat history

[adrianlyjak]

Adds session history

• Session metadata is stored on the client in indexed db
• Conversation history is stored in the workflow state
• Adds a sidebar with timestamped conversation sessions

Updates the UI a bit to look better with the sidebar. Also adds dark/light mode detection

Future things that need fixing or improving:

• Need to delete backend workflows when the frontend is deleted
• Should synchronize and detect deleted conversations on the client, or alternately entirely query the workflows from the server (needs further features added to workflow server)
• Should "sleep" inactive workflows to save resources on the server
• The workflow list API is querying details of all the active workflows individually. Was noticing some potential bugs related to this with a lot of parallel requests. Reloading history was getting buggy

[zhaotai]

what if index is already there and there is no cache in memory?

[adrianlyjak]

despite its name, create_index does an upsert operation