Add external plugin canvas-authoring (#3745)

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

plugins/external.json

@@ -290,6 +290,31 @@
       "sha": "678c3468977889d5c50a0a5f33898b8d9638523a"
     }
   },
+  {
+    "name": "canvas-authoring",
+    "description": "Toolkit setup and Azure or counter starters for the host’s native `create-canvas` skill; skill-only, not a canvas extension.  Includes prebuilt packages and guidance for styles, sign in, subscriptions, telemetry, and more.",
+    "version": "0.1.1",
+    "author": {
+      "name": "Alex Weininger"
+    },
+    "repository": "https://github.com/microsoft/azure-dev-tools",
+    "license": "MIT",
+    "keywords": [
+      "canvas-authoring",
+      "toolkit",
+      "skills",
+      "development",
+      "azure",
+      "scaffolding",
+      "build"
+    ],
+    "source": {
+      "source": "github",
+      "repo": "microsoft/azure-dev-tools",
+      "path": "plugins/canvas-authoring",
+      "sha": "a6d394bbaa6fb1dc0151257a85cbac0de772b138"
+    }
+  },
   {
     "name": "catalyst-by-zoho",
     "description": "Official GitHub Copilot plugin for Catalyst by Zoho — a full-stack serverless cloud platform. Includes skills covering services, SDKs, CLI workflows, architecture patterns, pricing, migration guides, and Zoho MCP resource management.",