Add Canvas Extensions website page (#1900)

Generate extensions data, add the extensions listing route/navigation, and include install URL copy actions pinned to the build commit SHA.

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

extensions/diagram-viewer/package.json

@@ -0,0 +1,9 @@
+{
+  "name": "diagram-viewer",
+  "version": "1.0.0",
+  "type": "module",
+  "main": "extension.mjs",
+  "dependencies": {
+    "@github/copilot-sdk": "latest"
+  }
+}