Route AI quick actions into request chat

[harryadel]

Summary

• Route Explain Request, Suggest Attack Vectors, and selected-text explanations into the existing request-scoped AI chat
• Automatically open the right-side chat pane and retain prior turns for follow-up questions
• Move Markdown and PDF export into the chat header and remove the obsolete one-shot explanation modal
• Add focused coverage for quick-action routing, automatic pane opening, request context, and follow-up history

Testing

• npm test -- tests/ai-chat-actions.test.js tests/llm-chat.test.js (4 passed)
• npm run package
• Full upstream suite: 170 of 171 tests pass; the unchanged network-parsing assertion for a Host-only request also fails on upstream/main

[greptile-apps]

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