fix: enforce semantic contrast across admin

src/components/admin/media-grid.tsx

@@ -103,9 +103,9 @@ export function AdminMediaGrid() {
       )}
 
       {loading ? (
-        <p className="text-xs text-gray-500 dark:text-gray-400">Loading…</p>
+        <p className="text-xs theme-text-muted dark:theme-text-muted">Loading…</p>
       ) : files.length === 0 ? (
-        <p className="text-xs text-gray-500 dark:text-gray-400">No images yet. Upload one above.</p>
+        <p className="text-xs theme-text-muted dark:theme-text-muted">No images yet. Upload one above.</p>
       ) : (
         <div className="grid grid-cols-[repeat(auto-fill,minmax(160px,1fr))] gap-3">
           {files.map((f) => (