Fix: Deploy frontend/ to GitHub Pages via Actions workflow

[Copilot]

Problem

GitHub Pages was serving from the repo root (which has README.md but no index.html), causing the site to display the README instead of the app.

Even after switching Settings → Pages → Source to "GitHub Actions", the site still showed README.md because this workflow didn't exist on main yet — so nothing was being deployed.

Fix

Adds .github/workflows/pages.yml which:

• Triggers on every push to main (and supports manual dispatch)
• Uploads only the frontend/ directory as the Pages artifact
• Deploys it to GitHub Pages so index.html is served at the site root

Steps to activate

1. Merge this PR
2. Go to Settings → Pages → Source and confirm it is set to "GitHub Actions" (if you already did this, leave it)
3. The workflow will run automatically on merge and deploy frontend/index.html as the site homepage

[Copilot]

Pull request overview

Adds a GitHub Actions workflow to deploy the static site located in frontend/ to GitHub Pages, ensuring Pages serves frontend/index.html at the site root rather than the repository README.

Changes:

• Introduces a Pages deployment workflow triggered on pushes to main and via manual dispatch.
• Configures GitHub Pages, uploads ./frontend as the Pages artifact, and deploys it using the standard deploy-pages action.

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