Add author attribution to Site Studio canvas (#2166)

Adds the author block to extensions/site-studio/canvas.json so the canvas
gallery shows attribution (by @ayangupt), matching other extensions.

Co-authored-by: Ayan Gupta <ayangupt@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

extensions/site-studio/canvas.json

@@ -3,6 +3,10 @@
   "name": "Site Studio",
   "description": "Plan, draft, and track a personal website section by section — a shared canvas where you and your agent author content, watch progress, and review every change.",
   "version": "1.0.0",
+  "author": {
+    "name": "Ayan Gupta",
+    "url": "https://github.com/ayangupt"
+  },
   "keywords": [
     "agent-collaboration",
     "content-authoring",