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>

site/layouts/_default/list.html

@@ -0,0 +1,24 @@
+{{ define "header" }}
+  <header>
+    <h1>{{ .Title }}</h1>
+    {{ with .Description }}<p>{{ . }}</p>{{ end }}
+  </header>
+{{ end }}
+
+{{ define "content" }}
+  <article role="main">
+    <section>
+      {{ range .Pages }}
+      <article>
+        <header>
+          <h2><a href="{{ .Permalink }}">{{ .Title }}</a></h2>
+          <p data-text="dim">
+            <time datetime="{{ .Date.Format "2006-01-02" }}">{{ .Date.Format "January 2006" }}</time>
+          </p>
+        </header>
+        {{ with .Summary }}<p>{{ . }}</p>{{ end }}
+      </article>
+      {{ end }}
+    </section>
+  </article>
+{{ end }}