[codex] Fix mobile chat input and profile links

[verkyyi]

Summary

• Replace the hero agent explainer with simple profile links sourced from resume profiles.
• Make the chat input render as a visible bounded field on narrow mobile viewports.
• Add a PR preview artifact workflow that builds web/dist for future pull requests.
• Update app and hero tests for the revised hero behavior.

Why

On mobile Safari-style layouts, the chat input could appear poorly because it was a transparent borderless input inside a compact flex row. The hero also still described the page as an agent, while this view should present plain social links such as LinkedIn and GitHub.

The repo only had a production GitHub Pages deployment for main; the new PR Preview workflow creates a lightweight staging artifact without adding hosting infrastructure or touching production deploys.

Validation

• npm test
• npm run build
• VITE_BASE_PATH=./ npm run build
• npx playwright test e2e/portfolio-layout.spec.ts
• Parsed .github/workflows/pr-preview.yml with PyYAML.
• Manual Playwright mobile check at 390x844: no horizontal overflow; input rendered 40px high with 16px text.

Note

GitHub only exposes/runs a newly added workflow after the workflow file exists on the default branch, so the PR Preview workflow will start producing artifacts for subsequent PRs after this lands.