fix(clipboard): use navigator.clipboard.writeText as primary, arboard as fallback — fixes silent failure on Linux/XWayland

src/lib/pages/FilesPage.svelte

@@ -118,7 +118,11 @@
   }
 
   function copyAll() {
-    if (fileTranscript) invoke("copy_to_clipboard", { text: fileTranscript }).catch(() => {});
+    if (fileTranscript) {
+      navigator.clipboard.writeText(fileTranscript).catch(() => {
+        invoke("copy_to_clipboard", { text: fileTranscript }).catch(() => {});
+      });
+    }
   }
 
   function handleExport(format) {