feat: panneau A propos elegant + retrait Editor POC

- Remplace Editor POC par A propos (sparkles) dans le menu header
- Modale About avec animation fade+scale, logo SVG, hero gradient
- Stats live: fichiers, vaults (API /health), tests (285)
- Stack techno: 12 badges (FastAPI, vanilla JS, Docker, etc.)
- Footer: date livraison, blague aleatoire (10 variantes humour)
- Touche d'humour: git push --force accidentels, CSS > backend
- Fermeture: bouton X, clic overlay, Escape
- initAboutModal dans sync.js + config.js export

frontend/js/legacy.js

@@ -25,7 +25,7 @@ import {
 } from './dashboard.js';
 
 // --- Re-exports from modules that already have these functions ---
-export { initSidebarTabs, initConfigModal, initHelpModal, initRecentTab, initEditorPocBtn } from './config.js';
+export { initSidebarTabs, initConfigModal, initHelpModal, initRecentTab, initAboutModal } from './config.js';
 export { initSyncStatus } from './sync.js';
 export { DashboardRecentWidget } from './dashboard.js';