chore: add Renovate config

Updates the actions used in the workflows (github-actions manager).
No automerge: there is no build to gate an update, and main only
reaches consumers when the vN tag is moved after a live test.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_011AgnQS6MHAGGoLNQDvv52d

renovate.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "timezone": "Europe/Berlin",
+  "enabledManagers": ["github-actions"],
+  "packageRules": [
+    {
+      "description": "No automerge: these repos have no build that could gate an update, and a change on main only reaches consumers when the templates session moves a vN tag after a live test in a consumer repo.",
+      "matchPackageNames": ["*"],
+      "automerge": false
+    }
+  ]
+}