Polish portfolio nav, add Resume page and backend-managed Contact form

[ryanbaumann]

Motivation

• Reduce the header footprint so the site header is a single-line shell (especially on mobile) and give visitors explicit Resume and Contact affordances.
• Stop exposing the owner's email in public HTML while keeping an easy contact path, and add a lightweight, persistent light/dark toggle to address the theme preference concern.
• Surface a resume-like summary and keep preview imagery honest (real screenshots where they exist; generated artifact cards only where no screenshot exists) to improve trust and reduce the “AI-generated” feel.

Description

• Added compact one-line header and a Theme toggle persisted to localStorage and injected a tiny inline script in portfolio/build.mjs, and added supporting styles in portfolio/style.css for the compact header, theme button, resume and contact shells.
• Extended portfolio/build.mjs to include Resume and Contact nav items, injected a resumePageContent() and contactPageContent() renderer for content/pages/resume.md and content/pages/contact.md, and replaced mailto: links with a /contact/ link; removed the exposed email key from portfolio/content/site.json.
• Implemented a backend /api/contact POST handler in gateway/server.js (handleContactRequest) that validates the form, reads the recipient from server-only env vars, and sends via Resend when RESEND_API_KEY and CONTACT_TO_EMAIL are configured, otherwise returns a safe setup 503 page; the route returns friendly HTML responses for success/error states.
• Updated copy and meta guidance: edited .agents/skills/portfolio-design/SKILL.md to allow the tiny explicit theme script, updated portfolio/content/pages/about.md to link to /contact/, and recorded the change in CHANGELOG.md and LEARNINGS.md; added portfolio/content/pages/resume.md and contact.md.

Testing

• npm run build in portfolio/ completed successfully and portfolio build-time metadata validation passed.
• node --check gateway/server.js succeeded and npm test in gateway/ passed (all gateway unit tests green).
• Repo-level build with node scripts/build-local.mjs completed and npm run smoke (dependency-free smoke test) passed (17 passed, 0 failed).
• Manual POST to POST /api/contact against a locally started gateway returned 503 as expected when mail env vars were not set, demonstrating safe fallback behavior.
• Notes/limitations: browser screenshot capture was not available in this environment because no Chromium/Playwright binary is installed; contact delivery requires RESEND_API_KEY and CONTACT_TO_EMAIL (and optional CONTACT_FROM_EMAIL) to be set in the deployment environment for emails to actually send.

---

Codex Task