Add GitHub Pages workflow to build and publish Typst write-up PDF

[Copilot]

This issue asks to host the project write-up on GitHub Pages and automatically compile the Typst source on each commit. This PR adds a dedicated Actions workflow to build the PDF and publish it as a Pages site artifact.

• Workflow: build + deploy write-up

  • Added .github/workflows/writeup-pages.yml.
  • Triggers on push, pull_request, and workflow_dispatch.
  • Uses typst-community/setup-typst@v4 to compile WriteUp/main.typ into site/main.pdf.

• Pages artifact and deployment

  • Uploads site/ via actions/upload-pages-artifact@v3.
  • Deploys with actions/deploy-pages@v4 on pushes to the repository default branch.
  • Includes required Pages permissions (pages: write, id-token: write) and a Pages-safe concurrency group.

• Hosted entrypoint

  • Generates site/index.html during the workflow.
  • Serves an embedded PDF viewer with a direct fallback link to main.pdf.

- name: Build PDF
  run: |
    mkdir -p site
    typst compile --root . WriteUp/main.typ site/main.pdf

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