feat: add Unflag to the sample table context menu

Below Mount/Unmount, acting on the selection like the queue actions.
Flagging happens by dropping rows on the Flagged chip; until now
there was no way back. Disabled when nothing in the selection is
flagged.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/aare/gui/panels/tell_sample_panel.py

@@ -318,6 +318,11 @@ class TellSamplePanel(QFrame):
         mount_action = menu.addAction("Mount")
         # Unmount moved here from the removed bottom-row button — same signal.
         unmount_action = menu.addAction("Unmount")
+        menu.addSeparator()
+        # Flagging happens by dropping rows on the Flagged chip; this is the
+        # only way back, so it lives here even though Flag does not.
+        unflag_action = menu.addAction(f"Unflag{count}")
+        unflag_action.setEnabled(any(s.db_id in self.table_model.flagged_ids for s in selected))
 
         action = menu.exec_(self.table_view.viewport().mapToGlobal(position))
 
@@ -331,6 +336,10 @@ class TellSamplePanel(QFrame):
         elif action == remove_queue_action:
             self.remove_from_queue.emit(SampleShortInfoList(s=selected))
             self.table_view.clearSelection()
+        elif action == unflag_action:
+            for s in selected:
+                self.table_model.set_flagged(s.db_id, False)
+            self.table_view.clearSelection()
 
     def header_context_menu(self, pos):
         header = self.table_view.horizontalHeader()