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/cards.css

@@ -322,6 +322,17 @@ button.favorite-star {
 	overflow: hidden;
 }
 
+/* Thumbnail image inside file-icon (grid and list views) */
+.file-icon .file-thumb {
+	position: absolute;
+	top: 0;
+	left: 0;
+	width: 100%;
+	height: 100%;
+	object-fit: cover;
+	z-index: 1;
+}
+
 .file-icon.image-icon::before {
 	content: "";
 	position: absolute;