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

src/routes/viewer/+page.svelte

@@ -194,7 +194,10 @@
 
   function copySegment(idx) {
     if (item?.segments?.[idx]) {
-      invoke("copy_to_clipboard", { text: item.segments[idx].text.trim() }).catch(() => {});
+      const text = item.segments[idx].text.trim();
+      navigator.clipboard.writeText(text).catch(() => {
+        invoke("copy_to_clipboard", { text }).catch(() => {});
+      });
     }
   }