chore: drop the inactive .drone.star Drone CI config

[oc-tmueller]

Closes the root cause behind #707.

Why

This repository migrated to GitHub Actions in #575, but .drone.star was left behind — unlike the sibling images, which deleted theirs in the same move: owncloud-docker/php#232, owncloud-docker/ubuntu#231, owncloud-docker/base#422. Of all non-archived repos in this org, only server and helm-charts still carry one.

Nothing executes it:

• .github/workflows/main.yml owns the whole pipeline — editorconfig lint, multiarch build, smoke test on status.php, Trivy with per-version ignore files, Docker Hub push and description sync.
• Its contents are ~18 months stale: it still builds 11.0.0-prealpha, 10.16.1 and 10.15.3 from download.owncloud.com, and pushes through registry.drone.owncloud.com.
• agents.md already told readers to ignore it.

It was not merely dead weight, though. owncloud-ops/renovate-presets:base carries a customManagers entry with fileMatch: ["(^|/)\\.drone\\.star$"] matching .+_IMAGE assignments, so all six image constants at the top of the file were live Renovate dependencies — the Dependency Dashboard (#241) lists them under regex (1) → .drone.star (6). That produced both manual noise (#707: mariadb 10.11 → 13.0) and, because the :docker preset automerges digest updates for mariadb|redis|ubuntu|owncloud/*, unattended commits to a file nobody runs (995265b, #659).

What

• Delete .drone.star (706 lines).
• Drop the now-unreachable .drone.yml entry from .gitignore — it only ever ignored the starlark-generated output, and nothing generates it any more.
• Remove the two .drone.star references from agents.md.

No CHANGELOG.md entry: the date-based changelog tracks published-image content, and the GHA migration itself (#575) added none either. Nothing about the built image changes here.

No CI coverage is lost

• Drone's lint pipeline ran buildifier on .drone.star itself, plus an editorconfig check that the reusable lint-editorconfig.yml now performs.
• Its shellcheck step globbed <base>/overlay/, which contains only .keep files — zero files were ever checked.
• The API/webUI behat pipelines targeted registry.drone.owncloud.com and the stale tarballs above; they cannot run.

The one pipeline never ported to Actions is the webUI/Selenium acceptance job. That is a pre-existing gap, tracked by #577 and in progress in #677 (api + cli). For anyone reviving it, the pipeline definition is def ui at line 543 of the file as it stood at its last commit:

git show 995265bea49320e979c4838bcd5cc8779f466967:.drone.star

Verification

• grep -rni drone . --exclude-dir=.git → one hit, the historical CHANGELOG.md:45 entry from 2020, which stays.
• grep -rn drone .github/ → no hits; no workflow, Dependabot or Renovate config points at the file.
• editorconfig-checker run locally over the result: 0 errors found, 19 files checked (and confirmed able to fail, by probing it with a trailing-whitespace file).
• After merge, Dependency Dashboard Dependency Dashboard #241 should lose its whole regex (1) → .drone.star (6) section on Renovate's next run, leaving only dockerfile (2) and github-actions (2).

🤖 Generated with Claude Code