ci: use nix build for page artifacts

Author: TerrorJack

.github/workflows/build.yml

@@ -38,6 +38,15 @@ jobs:
         run: |
           nix develop --command bash -c "cd frontend && exec ./build.sh --low-memory-unused --strip-dwarf --converge -O4 -Oz"
 
+      - name: upload-pages-artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: frontend/dist
+          retention-days: 90
+
+      - name: deploy-pages
+        uses: actions/deploy-pages@v4
+
   ghcup-build:
     name: ghcup-build
     runs-on: ubuntu-24.04
@@ -134,12 +143,3 @@ jobs:
         run: |
           cd frontend
           ./build.sh --low-memory-unused --strip-dwarf --converge -O4 -Oz
-
-      - name: upload-pages-artifact
-        uses: actions/upload-pages-artifact@v3
-        with:
-          path: frontend/dist
-          retention-days: 90
-
-      - name: deploy-pages
-        uses: actions/deploy-pages@v4