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/shortcodes/wikilink.html

@@ -0,0 +1,20 @@
+{{- /*
+  wikilink shortcode — renders an internal link with ASW data-wikilink attribute.
+  
+  Usage:
+    {{< wikilink "Display Text" "/path/to/page/" >}}
+  
+  Param 0 (required): display text
+  Param 1 (optional): href path. Defaults to /display-text-slugified/
+  
+  Examples:
+    {{< wikilink "My Note" >}}
+    → <a href="/my-note/" data-wikilink>My Note</a>
+    
+    {{< wikilink "My Note" "/vault/my-note/" >}}
+    → <a href="/vault/my-note/" data-wikilink>My Note</a>
+*/ -}}
+{{- $text := .Get 0 -}}
+{{- $slug := $text | lower | replace " " "-" -}}
+{{- $href := .Get 1 | default (printf "/%s/" $slug) -}}
+<a href="{{ $href | relURL }}" data-wikilink>{{ $text }}</a>