Add CI workflows and GitHub Pages deployment for web app

[MichaelSScott]

Motivation

• Provide automated validation for the monorepo on PRs/pushes and enable automatic deployment of the static frontend to GitHub Pages.
• Ensure the Vite-built frontend resolves assets/routes correctly when served from https://<user>.github.io/<repo>/.

Description

• Add CI workflow at .github/workflows/ci.yml that installs web dependencies with pnpm, runs web tests and builds the frontend, and installs API deps then runs pytest for apps/api.
• Add deploy workflow at .github/workflows/deploy-pages.yml that builds apps/web and deploys apps/web/dist to GitHub Pages, and forwards VITE_API_BASE_URL from repository variables during the build.
• Update apps/web/vite.config.ts to set base automatically when running in GitHub Actions so router and static assets resolve under the repo path.
• Document the CI/CD and GitHub Pages steps, Pages limitations, and VITE_API_BASE_URL configuration in README.md.

Testing

• Ran pytest in apps/api and all tests passed (6 passed).
• Attempted pnpm install/web build/tests locally but pnpm install failed in this environment with ERR_PNPM_FETCH_403 due to npm registry authorization, so web tests/build could not be executed here.

---

Codex Task