Add key-free MCP tools, human approvals and opt-in assistant

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+  <section class="panel"><h2>Assistant and AI agents</h2><p>Use your own model endpoint, or review a proposed MCP action. Nothing is sent to a model until you opt in.</p><a href="/assistant">Open assistant</a></section>
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       <div class="shelf-head"><h2>Send to Frame</h2></div>