feat: PR preview deployments on GitHub Pages

[Copilot]

• Update next.config.ts: change output to export, add dynamic basePath via NEXT_PUBLIC_BASE_PATH env var, add images.unoptimized: true
• Update .github/workflows/gh-pages.yml: switch from Pages-API deployment to branch-based deployment using JamesIves/github-pages-deploy-action@v4; set NEXT_PUBLIC_BASE_PATH=/quartett-meister; preserve pr-preview dir with clean-exclude
• Create .github/workflows/preview.yml: build with PR-scoped basePath (/quartett-meister/pr-preview/pr-{number}), deploy/remove using rossjrw/pr-preview-action@v1
• Fix PR preview not loading: add .nojekyll to gh-pages root in preview.yml — JamesIves places .nojekyll inside the deployed folder (pr-preview/pr-N/.nojekyll), not the branch root, so Jekyll was silently blocking _next/ asset directories

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[github-actions]

PR Preview Action v1.8.1
Preview removed because the pull request was closed.
2026-03-12 18:48 UTC

[Lotes]

@copilot The preview deploy of this PR is not reachable, find out why: https://lotes.github.io/quartett-meister/pr-preview/pr-14/

[Copilot]

@copilot The preview deploy of this PR is not reachable, find out why: https://lotes.github.io/quartett-meister/pr-preview/pr-14/

Found the root cause (commit 03ad946):

JamesIves/github-pages-deploy-action@v4 creates .nojekyll inside the source folder being deployed (out/.nojekyll). Because rossjrw/pr-preview-action deploys to a target-folder (pr-preview/pr-14), the .nojekyll file landed at pr-preview/pr-14/.nojekyll in the gh-pages branch — not at the branch root. GitHub Pages runs Jekyll by default when there's no .nojekyll at the root, and Jekyll silently blocks every directory whose name starts with _. Next.js puts all JS and CSS under _next/, so the page HTML loaded (the "Lade…" spinner was served) but every script and stylesheet was 404'd.

Fix: two new steps in preview.yml before rossjrw/pr-preview-action:

1. Create a temp dir containing only an empty .nojekyll file
2. Deploy that dir to the gh-pages branch root via JamesIves/github-pages-deploy-action@v4 with clean: false (adds .nojekyll without touching anything else)

The next time the PR preview workflow runs (on the next push to this branch) the preview at https://lotes.github.io/quartett-meister/pr-preview/pr-14/ should be fully functional.