fix(metablog-ui): site.html uses canonical sbx_token key (ref #103)

Match the rest of the SecuBox Hub codebase (index.html, login.html,
shared/api-utils.js, every other module) which reads localStorage
under 'sbx_token'. The plan's heredoc had 'jwt' which would have
caused an infinite login redirect on every drill-in page load.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/secubox-metablogizer/www/metablogizer/site.html

@@ -131,7 +131,7 @@
         const API = '/api/v1/metablogizer';
 
         function headers() {
-            const t = localStorage.getItem('jwt');
+            const t = localStorage.getItem('sbx_token');
             return t ? { 'Authorization': `Bearer ${t}` } : {};
         }