feat: Slack platform + Claude-powered chat support widget

- Add Slack as customer-facing messaging platform (client, 4 MCP tools, dashboard card)
- Add /api/chat endpoint powered by Claude Haiku with SquareMCP system prompt
- Add embeddable chat-widget.js injected into all 3 sites (docs, app, www)
- Add ANTHROPIC_API_KEY, serve product/ as static files
- Update Platform type to include slack

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/platforms.html

@@ -284,5 +284,6 @@ Search Twitter for tweets mentioning "SquareMCP"</code></pre>
 Get the latest Telegram messages in my channel</code></pre>
 </div>
 
+<script src="https://hermes.squaremcp.com/chat-widget.js"></script>
 </body>
 </html>