Add production www layout for levkin.ca hosting.

- build:www maps / to spec and /folders to stack-folder
- Umami tracking via stats.levkin.ca
- nginx deploy config for site LXC

Co-authored-by: Cursor <cursoragent@cursor.com>

spec/index.html

@@ -24,7 +24,7 @@
   <a class="skip-link" href="#main">Skip to specification</a>
 
   <aside class="toc" aria-labelledby="toc-heading">
-    <a href="/" class="back">← all options</a>
+    <a href="/folders/" class="back">← folders</a>
     <p class="toc-doc-id">LK-SPEC-1.0</p>
     <h2 id="toc-heading" class="toc-title">Table of contents</h2>
     <nav aria-label="Specification sections">