Update AI chat project logo URL

Replace Wikipedia logo URL with official CockroachDB AI chat logo from cockroachlabs.com domain for better branding consistency.

Author: ebembi-crdb

src/current/_includes/head.html

@@ -147,7 +147,7 @@
   data-website-id="98d1a919-dfd3-4d54-a8a0-58c9094f57e5"
   data-project-name="CockroachDB"
   data-project-color="#6933FF"
-  data-project-logo="https://upload.wikimedia.org/wikipedia/en/3/31/Cockroach_Labs_Logo.png"
+  data-project-logo="https://www.cockroachlabs.com/img/ai-chat-logo-m.png"
   data-kapa-branding-hide="true"
   data-modal-title="CockroachDB AI"
   data-modal-disclaimer="This AI bot is experimental. Don't rely on it for production workloads. Always consult the official CockroachDB documentation. Interactions with this AI bot may be monitored or recorded, and your use of the AI bot is subject to the Cockroach Labs' [Terms of Use](https://www.cockroachlabs.com/website-terms-of-use/) and [Privacy policy](https://www.cockroachlabs.com/privacy/)."