gui: stop scrape-all dialog from reappearing after cancel

Cancelling the store scrape now closes the dialog and drops its reference
immediately, so queued progress signals can't re-show it (QProgressDialog
re-shows on setValue while a value is pending). _scraping stays true until
the worker finishes to prevent a second concurrent scrape.

app/gui.py

@@ -2320,7 +2320,7 @@ class StorePage(QWidget):
         thread.started.connect(worker.run)
         worker.progress.connect(self._on_scrape_progress)
         worker.finished.connect(thread.quit)
-        dlg.canceled.connect(worker.cancel)
+        dlg.canceled.connect(self._on_scrape_cancelled)
         worker.finished.connect(self._on_scrape_done)
         self._scrape_thread = thread
         self._scrape_worker = worker
@@ -2328,6 +2328,19 @@ class StorePage(QWidget):
         self._workers.append(worker)
         thread.start()
 
+    def _on_scrape_cancelled(self):
+        worker = self._scrape_worker
+        if worker is not None:
+            worker.cancel()
+        dlg = self._scrape_dialog
+        if dlg is not None:
+            dlg.close()
+        # Drop the dialog reference so queued progress signals can't re-show it
+        # (QProgressDialog re-appears on setValue while a value is pending).
+        # Keep _scraping True until the worker actually finishes (_on_scrape_done)
+        # so a re-click doesn't spawn a second scrape while this one winds down.
+        self._scrape_dialog = None
+
     def _on_scrape_progress(self, done, total):
         dlg = self._scrape_dialog
         if dlg is not None: