Implements persistent/voluminous chat history on the Testar Agente screen:
- Prepare to store and load previous conversations (localStorage) for the selected agent
- Create structure for conversations and messages
- Load existing conversations on mount and save changes
- Add support to create new conversations and load them when selected
Update the TestPrompt page to TestAgent. It now features a select dropdown for choosing an agent and a chat interface. The previous prompt and model selection components have been removed.