feat: Slack alerts for chat widget escalations + support@ email polling

- notifications/slack.ts: added sendChatEscalationAlert (fires when visitor
  asks about pricing, demo, help, or a human) and sendSupportEmailAlert
- email-poller.ts: polls support@squaremcp.com every 5 min via IMAP,
  deduplicates with Redis (support📧alerted_uids), fires Slack alert
  for each new unseen message
- index.ts: detectEscalation() scans last user message for trigger phrases;
  chat endpoint fires alert fire-and-forget after responding; startEmailPoller()
  called on server boot

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

src/email-poller.ts

@@ -0,0 +1,42 @@
+import { searchMessages } from './imap.js';
+import { sendSupportEmailAlert } from './notifications/slack.js';
+import redis from './redis.js';
+
+const REDIS_KEY = 'support:email:alerted_uids';
+const POLL_INTERVAL_MS = 5 * 60 * 1000;
+
+async function pollSupportInbox() {
+  try {
+    const messages = await searchMessages('', 20, 'sqcp_support');
+    if (messages.length === 0) return;
+
+    const alreadyAlerted = await redis.sMembers(REDIS_KEY);
+    const alerted = new Set(alreadyAlerted);
+
+    for (const msg of messages) {
+      if (msg.seen) continue;
+      const key = String(msg.uid);
+      if (alerted.has(key)) continue;
+
+      await sendSupportEmailAlert({
+        uid: msg.uid,
+        subject: msg.subject,
+        from: msg.from,
+        date: msg.date,
+      });
+
+      await redis.sAdd(REDIS_KEY, key);
+      // Keep the set from growing unbounded — trim to last 500 UIDs
+      await redis.expire(REDIS_KEY, 60 * 60 * 24 * 30); // 30-day TTL
+      console.log(`[email-poller] alerted on uid=${msg.uid} from=${msg.from}`);
+    }
+  } catch (err) {
+    console.error('[email-poller] poll error:', (err as Error).message);
+  }
+}
+
+export function startEmailPoller() {
+  console.log('[email-poller] starting — polling support@squaremcp.com every 5 min');
+  pollSupportInbox();
+  setInterval(pollSupportInbox, POLL_INTERVAL_MS);
+}