Add multi-turn conversation support to explain sidepanel

[Copilot]

Implements chatbot pattern from AI SDK to enable follow-up questions in the explain sidepanel. Users can now ask clarifying questions without restarting the explanation flow.

Changes

New chat wrapper (logic/explain/chat.ts)

• useExplainChat composable maintains message history and supports multi-turn conversations
• Converts internal Message[] to AI SDK's ModelMessage format for streaming
• Preserves tool calling support (e.g., getPageContent)

Updated sidepanel UI (entrypoints/explain.sidepanel/Explain.vue)

• Conversation view replaces single-response display
• Follow-up input with textarea and send button
• Keyboard shortcuts: Enter to send, Shift+Enter for newline
• Save conversation feature includes full message history

Styling (Explain.scss)

• Chat-specific styles for message containers and role labels
• User messages: --color-surface-2, Assistant: --color-surface

Usage

import { useExplainChat } from "~/logic/explain";

const chat = useExplainChat({
  modelString: "openai:gpt-4",
  providers: llmProviders.value,
  onUpdate: (update) => {
    if (update.messages) messages.value = update.messages;
  },
});

// Initial question
await chat.sendMessage("Explain this code", tabId);

// Follow-up with context
await chat.sendMessage("Can you give an example?");

Type fixes

• Fixed error handling in chat.ts and index.ts to properly type-cast unknown errors
• Added type assertion for modelString in provider-registry.ts

Original useExplainAgent remains available for backward compatibility.

Original prompt

使用 https://ai-sdk.dev/docs/ai-sdk-ui/chatbot 进一步包装 useExplainAgent 以使得用户可以在 explain.sidepanel 中进一步追问

Created from VS Code via the GitHub Pull Request extension.

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