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/css/components/fileList.css

@@ -145,6 +145,9 @@
 
 .file-item .file-icon.image-icon {
 	background-color: #e0f2fe;
+	position: relative;
+	overflow: hidden;
+	border-radius: 4px;
 }
 
 .file-item .file-icon.image-icon i,