refactor: restructure repo into src/ site/ dist/ vendor/ packs/

Separate framework source from website:
- src/layers/ + src/main.css: CSS framework source (was assets/css/)
- site/: Hugo website (content/, layouts/, hugo.toml)
- dist/: built output (asw.css, asw.min.css)
- vendor/open-props/: vendored dependency with version tracking
- Hugo module mounts: dist/ → static, site runs from site/

Build: hugo --source site/ passes (105 pages).
npm run build produces dist/asw.css.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitignore

@@ -1,5 +1,14 @@
 node_modules/
 .hugo_build.lock
-resources/_gen/
-public/
 build.log
+postcss.dev.config.js
+dev.sh
+
+# Hugo output and cache (all under site/)
+site/public/
+site/resources/
+site/hugo_stats.json
+
+# dev.sh generated output (under site/)
+site/static/css/
+site/static/vendor/