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>

product/app/index.html

@@ -194,6 +194,17 @@
           <button class="btn btn-connect" data-platform="whatsapp">Connect</button>
         </div>
 
+        <!-- Slack -->
+        <div class="platform-card" data-platform="slack">
+          <div class="platform-icon" style="background:#4a154b;">💬</div>
+          <div class="platform-info">
+            <h3>Slack</h3>
+            <p class="platform-desc">Send messages to channels</p>
+            <span class="status-badge disconnected">Not connected</span>
+          </div>
+          <button class="btn btn-connect" data-platform="slack">Connect</button>
+        </div>
+
         <!-- Email -->
         <div class="platform-card" data-platform="email">
           <div class="platform-icon" style="background:#ea4335;">✉️</div>
@@ -271,5 +282,6 @@
 
 <script src="https://cdn.jsdelivr.net/npm/chart.js@4/dist/chart.umd.min.js"></script>
 <script src="app.js"></script>
+<script src="https://hermes.squaremcp.com/chat-widget.js"></script>
 </body>
 </html>