Improve UI

[benmvp]

Problem

The UI has been kind of clunky with how things are displayed and the fact that input loses focus

Solution

• Improved the display by merging as much content together so that they are <p> tags instead of completely new <Markdown> components
• Memoize the chat UI and input so that focus remains on the input after submissions
• Pass Shein price to assistant so that it can make better pricing decisions
• Request Best Buy product data for requested item IDs instead of relying on an already-populated cache
• Add mock data for Best Buy
• Improve system instructions