Create deploy.yml

[AvatarMiiDe]

What Was Designed
The workflow (.github/workflows/deploy.yml) is set up to provide the following:

Build on PRs: Automatically triggers mdbook test and mdbook build to catch broken links and code test failures in your mdBook docs before they can be merged.
PR Preview Artifacts: On PRs, the built book/ directory is zipped and uploaded using actions/upload-artifact@v4 as site-preview. Reviewers can download the built HTML artifacts directly from the PR's "Checks" tab to preview the visual appearance of the documentation locally before approving the merge.
GitHub Pages Deployment: On merges to main, the deploy job leverages GitHub's native actions/deploy-pages@v4 workflow. This integrates smoothly with GitHub's newer Actions-based Pages deployment system.

NOTE: Go to your repository settings in GitHub: Settings > Pages > Build and deployment. Make sure the Source is set to GitHub Actions, rather than "Deploy from a branch".

Close #254

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[salazarsebas]

This workflow runs mdbook build/mdbook test, but this repo doesn't have an mdBook project (no book.toml, no src/ book directory) — as written, this job will fail immediately on merge. #254 explicitly scopes this pipeline to a separate cougr-site repo. We're actually bringing that scaffold into this monorepo as a cougr-site/ folder (see #284) — could you hold this PR until that lands, then point working-directory/paths at the new folder? Once that's in place the deploy-to-Pages + PR-preview design here should work as intended.

[salazarsebas]

Good starting point for #254. Two things to align on: (1) the issue asks for a 'shareable preview build' for PRs — right now this uploads a plain workflow artifact, which requires manual download rather than a link reviewers can click. Could you look at something like a preview subdomain/path or a bot comment with a direct link? (2) #284 also adds a .github/workflows/deploy-site.yml for the same purpose — worth coordinating so we don't land two deploy pipelines. Please also rebase onto current main.