fix(thumbnails): display thumbnails in file grid/list and fix WOPI intercepting all file opens

wopiEditor.canEdit() is async but was called without await, so the
returned Promise was always truthy — routing every file click to the
WOPI editor (which 404'd). Made openFile() async and added await in
both ui.js and inlineViewer.js.

Added <img> thumbnail elements to _createFileCard() and
_createFileItem() for image files, loading from
/api/files/{id}/thumbnail/icon with lazy loading and error fallback.

static/js/features/files/inlineViewer.js

@@ -88,11 +88,11 @@ class InlineViewer {
     console.log('Inline viewer initialized');
   }
   
-  openFile(file) {
+  async openFile(file) {
     console.log('Opening file:', file);
 
     // WOPI editor intercept: open Office documents in the WOPI editor
-    if (window.wopiEditor && window.wopiEditor.canEdit(file.name)) {
+    if (window.wopiEditor && await window.wopiEditor.canEdit(file.name)) {
         window.wopiEditor.openInModal(file.id, file.name, 'edit');
         return;
     }