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/index.html

@@ -0,0 +1,30 @@
+{{ define "title" }}{{ .Site.Title }}{{ end }}
+
+{{ define "header" }}
+  <header>
+    <hgroup>
+      <h1>{{ .Site.Title }}</h1>
+      <p>{{ .Site.Params.description | default "An agent-first approach to web generation." }}</p>
+    </hgroup>
+  </header>
+{{ end }}
+
+{{ define "content" }}
+  <article role="main">
+    <section>
+      <h2>Recent</h2>
+      {{ range first 10 .Site.RegularPages }}
+      <article>
+        <header>
+          <h3><a href="{{ .Permalink }}">{{ .Title }}</a></h3>
+          <p data-text="dim">
+            <time datetime="{{ .Date.Format "2006-01-02" }}">{{ .Date.Format "January 2006" }}</time>
+            {{ with .Params.eyebrow }} · {{ . }}{{ end }}
+          </p>
+        </header>
+        {{ with .Summary }}<p>{{ . }}</p>{{ end }}
+      </article>
+      {{ end }}
+    </section>
+  </article>
+{{ end }}