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>

src/main.css

@@ -0,0 +1,24 @@
+/* ASW — Agentic Semantic Web Framework
+ * Entry point: Open Props foundation + ASW layer stack
+ * PostCSS-import resolves all @imports at build time
+ *
+ * NOTE: ALL @import statements must come first.
+ * postcss-import drops any @import that follows a rule.
+ */
+
+/* 1. Open Props foundation */
+@import "open-props/open-props.min.css";
+@import "open-props/media.min.css";
+
+/* 2. Framework layers */
+@import "./layers/00-reset.css";
+@import "./layers/01-asw.css";
+@import "./layers/02-semantic.css";
+@import "./layers/03-components.css";
+@import "./layers/04-data-attrs.css";
+@import "./layers/05-utilities.css";
+@import "./layers/06-charts.css";
+@import "./layers/07-chroma.css";
+@import "./layers/08-layout.css";
+@import "./layers/08a-essay.css";
+@import "./layers/09-landing.css";