chore: activate dependabot

.github/dependabot.yml

@@ -1,11 +1,20 @@
-# To get started with Dependabot version updates, you'll need to specify which
-# package ecosystems to update and where the package manifests are located.
-# Please see the documentation for all configuration options:
-# https://docs.github.com/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+# The ecosystem was left as the template's empty string, which makes the whole
+# file inert - Dependabot parses it, matches nothing, and reports nothing. This
+# repo is TypeScript with a package.json at the root, and it also pins GitHub
+# Actions across five workflows.
 
 version: 2
 updates:
-  - package-ecosystem: "" # See documentation for possible values
-    directory: "/" # Location of package manifests
+  - package-ecosystem: "npm"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      # One PR a week for the routine bumps rather than one per package.
+      npm-minor-and-patch:
+        update-types: ["minor", "patch"]
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
     schedule:
       interval: "weekly"