feat(chat): upgrade to full agentic demo bot (Option B)

Chat widget now runs a live tool-use loop via Claude Haiku. Exposes
slack, discord, and telegram demo tools — bot can actually send messages
and read channels to prove the platform works in real time. Widget shows
a purple pill with tool names when the agent calls a live platform.

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

src/index.ts

@@ -1988,8 +1988,8 @@ app.post('/api/chat', async (req, res) => {
     return;
   }
   try {
-    const reply = await handleChat(messages);
-    res.json({ reply });
+    const { reply, toolsUsed } = await handleChat(messages);
+    res.json({ reply, toolsUsed });
   } catch (err) {
     console.error('[chat] error:', (err as Error).message);
     res.status(500).json({ error: 'Chat unavailable' });