feat: add GitHub Pages deploy workflow and update docs (Issue#5)

[seanseannery]

Key Changes

• Add .github/workflows/pages.yml: GitHub Actions workflow that deploys the site/ directory to GitHub Pages on push to main (path-filtered to site/**) and supports manual dispatch via workflow_dispatch.
• Update README.md: add website link (seanseannery.github.io/opsfile) below the H1 heading.
• Update AGENTS.md: add site/ entry to the directory structure section.

Why do we need this?

Closes Issue #5. The project has a static landing page in site/ but no automated deployment pipeline. This workflow wires up GitHub Pages deployment so the site is automatically published whenever site/ content is updated on main.

New modules or other dependencies introduced

None. Uses only official GitHub Actions: actions/checkout@v4, actions/configure-pages@v5, actions/upload-pages-artifact@v3, actions/deploy-pages@v4.

How was this tested?

• Workflow YAML validated against the GitHub Actions schema and the Pages deployment pattern from GitHub's official documentation.
• README and AGENTS.md changes reviewed visually to confirm correct placement and formatting.
• No Go code changed; make lint and make test not required for this change.