docs: add 'Custom Modes in Roo Code' tutorial video

Author: Your Name

docs/tutorial-videos.json

@@ -8,6 +8,10 @@
       "id": "g9sq25ECJMQ",
       "title": "Roo-Code v3.8 UPDATE: The Best FREE Autonomous AI Coding Agent Just Got BETTER!"
     },
+    {
+      "id": "qgqceCuhlRA",
+      "title": "Custom Modes in Roo Code | Official Tutorial "
+    },
     {
       "id": "mwJx5QI2c0o",
       "title": "You’re Overpaying for AI Coding | Roo Code System Prompt Override"