Add PR preview workflow for GitHub Pages

- Deploy PR previews to /pr-preview/pr-{number}/ subdirectory
- Automatic cleanup when PR is closed
- Uses rossjrw/pr-preview-action for deployment
- Builds with correct base path for preview URL

Author: neuromechanist

.github/workflows/pr-preview.yml

@@ -0,0 +1,73 @@
+name: PR Preview
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened, closed]
+
+permissions:
+  contents: write
+  pull-requests: write
+
+concurrency: preview-${{ github.ref }}
+
+jobs:
+  build-preview:
+    if: github.event.action != 'closed'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+        with:
+          lfs: true
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+          cache: 'npm'
+          cache-dependency-path: frontend/package-lock.json
+
+      - name: Install dependencies
+        working-directory: frontend
+        run: npm ci
+
+      - name: Copy static assets
+        working-directory: frontend
+        run: |
+          mkdir -p public/thumbnails public/downsampled public/annotations/nsd
+          cp -r ../data/thumbnails/* public/thumbnails/ 2>/dev/null || echo "No thumbnails to copy"
+          cp -r ../images/downsampled/* public/downsampled/ 2>/dev/null || echo "No images to copy"
+          cp -r ../annotations/nsd/*.json public/annotations/nsd/ 2>/dev/null || echo "No annotations to copy"
+
+      - name: Build Next.js site
+        working-directory: frontend
+        env:
+          # Set base path for PR preview subdirectory
+          NEXT_PUBLIC_BASE_PATH: /image-annotation/pr-preview/pr-${{ github.event.number }}
+        run: |
+          # Update next.config.js base path for preview
+          sed -i "s|'/image-annotation'|'/image-annotation/pr-preview/pr-${{ github.event.number }}'|g" next.config.js
+          npm run build
+
+      - name: Deploy PR Preview
+        uses: rossjrw/pr-preview-action@v1
+        with:
+          source-dir: frontend/out
+          preview-branch: gh-pages
+          umbrella-dir: pr-preview
+          action: auto
+
+  cleanup:
+    if: github.event.action == 'closed'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Cleanup PR Preview
+        uses: rossjrw/pr-preview-action@v1
+        with:
+          source-dir: frontend/out
+          preview-branch: gh-pages
+          umbrella-dir: pr-preview
+          action: remove