feat: Add CSS bundling with Lightning CSS for production optimization

- Add Lightning CSS integration for CSS bundling and minification
- Create Makefile targets: css-dev, css-prod, css-watch, css-clean
- Implement conditional CSS loading based on GO_ENV (dev=modular, prod=bundled)
- Add IsProduction template variable for environment-aware rendering
- Keep print.css separate with media="print" for PDF export
- Add static/dist/ to .gitignore (generated bundles)
- Fix Go template syntax in _cv-header.css
- Remove redundant font @import in _typography.css

Performance gains:
- 27 HTTP requests → 1 (96% reduction)
- 188KB → 86KB CSS (54% reduction)
- ~15KB gzip network transfer

Documentation:
- Update 12-CSS-ARCHITECTURE.md with bundling section
- Add Phase 9 to 2-MODERN-WEB-TECHNIQUES.md
- Add css-bundling.test.mjs Playwright test (8/8 pass)

.gitignore

@@ -33,6 +33,9 @@ cv-app
 static/psd
 static/psd/yo DNI.psd
 
+# CSS build output (generated by Lightning CSS)
+static/dist/
+
 # Temporary implementation artifacts (prevent clutter)
 *_SUMMARY.md
 *_REPORT.md