Migrate from Playwright postbuild prerendering to native framework SSG

[mgoldsborough]

Context

We added build-time prerendering using a Playwright postbuild script (scripts/prerender.ts) to solve the CSR-only SEO problem (bots see empty <div id="root"></div>). This works but is a workaround, not a native solution.

Current approach

• Playwright (already a dev dep for e2e tests) visits each static route after vite build
• Captures fully-rendered HTML and saves it to dist/<route>/index.html
• nginx's try_files serves pre-rendered HTML when available, falls back to SPA

Why migrate

• Playwright adds ~400MB to the Docker builder stage (Chromium install)
• Build times increase by 30-60s for the prerender step
• The script is custom code we maintain vs. a framework feature
• React Router 7 has built-in prerendering in Framework Mode

Options to evaluate

1. React Router Framework Mode - migrate from createBrowserRouter (Declarative Mode) to Framework Mode with react-router.config.ts. Gets native prerender: true support. Biggest migration but most "correct" path.
2. Astro - the nimblebrain marketing site already uses Astro. Could migrate mpak-web to Astro with React islands for interactive parts.
3. Keep Playwright - if the above are too costly, the current approach works fine.

Acceptance criteria

• Pre-rendered HTML for all static routes (/, /security, /about, /contact, etc.)
• Browse pages (/bundles, /skills) include initial API data in HTML
• No custom prerender script needed
• Chromium not required in Docker build