chore: adopt shared conf-renovate preset (v1.2.1) #15

1 / 4 tasks completed

3 tasks still to be completed

Task	Status
`renovate-config-validator --strict --no-global renovate.json5` passes locally (Node 24 + renovate@43, LOG_LEVEL=warn, exit 0).	Completed
After merge: Renovate dashboard onboards the new config cleanly.	Incomplete
First scheduled run produces PRs under preset group names (e.g. `gha-non-major`, plus ecosystem groups as applicable).	Incomplete
Next `conf-renovate` release auto-PRs a bump of `#v1.2.1` → `#v<next>`.	Incomplete