feat(backend): import Plane issues with their numbers, authors, and timestamps - #379

On December 2, 2026, GitHub will restrict `pull_request_target` on public repositories by default. To continue allowing the event trigger, configure an Actions policy. Learn more: https://gh.io/securely-using-pull_request_target#default-policy-for-pull_request_target

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: eps1lon/actions-label-merge-conflict@1df065ebe6e3310545d4f4c4e862e43bdca146f0. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/