Add info about the agent panel

[ethanpalm]

Documentation changes

When the agent is added back to the dashboard, this PR documents how to access it and info about the panel.

Part of https://linear.app/mintlify/issue/DOC-213/autopilot-launch-docs

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✅ Technical accuracy

• Code examples work as written
• Commands and configurations are correct
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• Prerequisites and requirements are accurate

✅ Clarity and completeness

• Instructions are clear and easy to follow
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✅ User experience

• A new user could follow these docs successfully
• Common gotchas or edge cases are addressed
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Note

Documents how to use the agent panel in the dashboard (access + views) and refines Slack integration steps and wording.

• Docs (ai/agent.mdx):
  • Dashboard usage: Add section on accessing the agent panel (keyboard shortcuts, Ask agent button, mobile/desktop behavior) and describe panel views (Chat, History, Settings).
  • Slack setup: Clarify wording and step naming (e.g., "In the Slack integration section, click Connect") and minor copy edits.

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