fix: graph.js syntax error at line 768 — template literal inside single quotes

- Line 768: changed to string concatenation in ternary expression
- Verified: 0 remaining ${t(...)} inside single quotes in graph.js, sync.js, ai.js

frontend/js/graph.js

@@ -765,7 +765,7 @@ export const GraphViewManager = {
       if (hit) {
         this._canvas.style.cursor = 'pointer';
         this._canvas.title = hit.node.type === 'file'
-          ? `📄 ${hit.node.name} (${t('graph.click_to_open')}${e.ctrlKey ? ', ${t('graph.ctrl_hover_preview_short')}' : ''})`
+          ? `📄 ${hit.node.name} (${t('graph.click_to_open')}${e.ctrlKey ? ', ' + t('graph.ctrl_hover_preview_short') : ''})`
           : `📁 ${hit.node.name} (cliquer pour explorer)`;
         
         // Ctrl+hover: fetch content preview for file nodes