Add dependabot npm config for s3-browser extension

The previous edit inserted the new npm ecosystem entry at the wrong
YAML indentation level, leaving /assets with an empty ignore list
and nesting the s3-browser entry incorrectly.

Fix: restore the live_toast ignore under /assets, and add
.pi/extensions/s3-browser as a proper top-level updates entry.

.github/dependabot.yml

@@ -44,6 +44,13 @@ updates:
   - cloud8421
   ignore:
   - dependency-name: "live_toast"
+- package-ecosystem: npm
+  directory: ".pi/extensions/s3-browser"
+  schedule:
+    interval: daily
+  open-pull-requests-limit: 10
+  assignees:
+  - cloud8421
 - package-ecosystem: docker
   directory: /
   schedule: