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)

templates/index.html

@@ -109,8 +109,12 @@
     <!-- Using unpkg CDN (more reliable than code.iconify.design) -->
     <script src="https://cdn.jsdelivr.net/npm/iconify-icon@2.1.0/dist/iconify-icon.min.js"></script>
 
-    <!-- CSS - Modular structure with native @import -->
+    <!-- CSS - Conditional loading: bundled in production, modular in development -->
+    {{if .IsProduction}}
+    <link rel="stylesheet" href="/static/dist/bundle.min.css">
+    {{else}}
     <link rel="stylesheet" href="/static/css/main.css">
+    {{end}}
     <!-- Print styles - loaded separately, only applied when printing -->
     <link rel="stylesheet" href="/static/css/print.css" media="print">