chore(ci): adopt the central Renovate preset

[TheMeinerLP]

Proposed changes

Split out of #143 so the Renovate migration lands on its own.

renovate.json here predates the org standard — it extends config:base directly and hand-rolls what the central preset already provides:

{
  "extends": ["config:base", ":semanticCommitsDisabled"],
  "rebaseWhen": "conflicted",
  "labels": ["Renovate"],
  "packageRules": [{ "matchUpdateTypes": ["patch"], "automerge": true }]
}

The central preset brings config:recommended as its base, plus patch automerge, semantic commit messages, a renovate label, Europe/Berlin timezone, office-hours scheduling (schedule:officeHours + schedule:automergeOfficeHours) and vulnerability alerts. The local copies are therefore redundant rather than additive, and they drift as the preset evolves.

:semanticCommitsDisabled was actively harmful here. Release Please parses Conventional Commits to decide the version bump and to build the changelog, so every Renovate merge landed without a type and produced neither. That matches what main's history looks like — Update dependency net.onelitefeather:mycelium-bom to v1.8.2 (#136), Update Gradle to v9.7.1 (#134) and so on, none of which Release Please can classify.

Two notes on the details

The team argument. :default(...) names the team the preset assigns as reviewer on every Renovate PR — without it, PRs get no reviewer. The org convention is <team>-maintainers, but the slug that actually exists for Vulpes is vulpes-maintainer (singular). Verified against orgs/OneLiteFeatherNET/teams; it's also what Vulpes-Backend already uses.

The patch-automerge rule is dropped, not carried over, because the preset covers it. ℹ️ Vulpes-Backend still carries that leftover packageRules block — worth cleaning up there separately.

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)

CI configuration only — none of the categories above fit precisely; no application code is touched.

Checklist

• I have read the CONTRIBUTING.md
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

No tests: this is a Renovate config file, validated by JSON parse and by the preset reference matching the org's canonical form. Its real effect only shows on Renovate's next run against main.

Further comments

Branched directly off main, so this is independent of #143 and the two can merge in either order.