dependabot-enable-triggers-immediate-pr-storm

Adding .github/dependabot.yml to a repo fires the first cron cycle within hours, opening one PR per ecosystem+group combination (9 PRs in this case). If not triaged immediately, these clutter origin branches and create noise. Enable dependabot only when ready to triage, or set open-pull-requests-limit: 0 and raise it only during deliberate dependency refresh windows.