chore: adopt org-wide Renovate config

[bigpuritz]

Summary

Replaces this repo's missing Renovate config with a one-line extends of the new org default at plugwerk/.github. From the next Renovate run forward, this repo gets the same considered defaults that plugwerk/plugwerk has been using:

• config:recommended + helpers:pinGitHubActionDigests
• Schedule: before 6am every weekday, Europe/Berlin
• Dependency Dashboard issue, label chore
• GitHub Actions: minor/patch grouped, majors split, all SHA-pinned
• Dockerfile: base-image digest grouping
• npm: minor/patch grouped, majors split per-package, exact-version pin

There are no repo-specific overrides today — examples follows the JVM stack but does not pin a specific JDK version like the main server, and there is no React/MUI surface that would need extra grouping. If that changes later, the override goes here in the same renovate.json alongside the extends.

Blocked by

• chore: bootstrap plugwerk/.github with org-wide defaults .github#1 — the org default config must be on main of plugwerk/.github before Renovate can resolve extends: ["github>plugwerk/.github"]. Until then, Renovate logs Cannot find preset's package and falls through to its built-in defaults — the existing behaviour, no regression.

Verification after merge

1. Wait for the next Renovate run (cron is 04:00 UTC weekdays; or trigger manually if a self-hosted workflow is added later).
2. Open the Renovate Dependency Dashboard issue this repo will create. Under "Detected dependencies" the resolved config should reflect the org rules (e.g. npm-deps grouping, github-actions SHA pinning).
3. Existing open Renovate PRs (if any) may be re-created with new branch names because grouping/slugs change. Mitigation: review and merge or close any open Renovate PRs in this repo before merging this PR.

Type of Change

• CI/Build

AI Agent Disclosure

• This PR was authored by an AI agent (Claude Opus 4.7)