Fix Pages deploy workflow by replacing failing Nix flake build path

[Copilot]

Pages deploys were failing in CI after runner/environment changes exposed a brittle Nix path (buildBunPackage missing in resolved nixpkgs). This updates the workflow to use the repo’s canonical Node/Vite build path while keeping deploy semantics unchanged (push to main + workflow_dispatch).

• Root cause removed

  • Eliminates dependence on nix build .#site for Pages artifact generation.
  • Avoids failures tied to flake evaluation/package attr drift in upstream nixpkgs.

• Build pipeline change (workflow-only)

  • Replaces Nix bootstrap/build steps with:
    • actions/setup-node@v4 (Node 22)
    • npm ci
    • npm run build
  • Publishes ./dist directly via actions/upload-pages-artifact@v3.

• Trigger scope preserved

  • Keeps production deploy trigger scope as push on main (plus workflow_dispatch).
  • Removes temporary branch-only trigger used during CI iteration.

- name: Setup Node.js
  uses: actions/setup-node@v4
  with:
    node-version: 22
    cache: npm

- name: Install dependencies
  run: npm ci

- name: Build site
  run: npm run build

- name: Upload artifact
  uses: actions/upload-pages-artifact@v3
  with:
    path: ./dist