fix: race condition on custom styles loading + misc cleanup

Guard watcher-triggered renders in usePreviewRenderer until first
explicit render completes, preventing premature renders with default
styles. Also: disable Contenu tab, update content/blueprints, add
global disabled button styles, minor formatting.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

public/site/blueprints/pages/projet.yml

@@ -7,17 +7,17 @@ columns:
       fields:
         type: fields
         fields:
-          subtitle: 
+          subtitle:
             label: Sous-titre
             type: text
             width: 1/2
-          cover: 
+          cover:
             label: Image de couverture
             type: files
             multiple: false
             width: 1/2
       pages:
-        label: Narratives
+        label: Récits
         type: pages
         template: narrative
   sidebar:
@@ -26,6 +26,3 @@ columns:
       files:
         label: Fichiers
         type: files
-
-
-