style: expanded help overlay opens top center, under the badge

The '?' badge moved to the top middle but the cheat sheet still
opened bottom-left, sending the mouse across the view to close it.
The overlay now drops in where the badge was.

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

src/aare/gui/widgets/camera_image.py

@@ -1150,7 +1150,9 @@ class SampleCameraImageLabel(QGraphicsView):
             + padding * 2
         )
 
-        bg_rect = QRectF(18, max(18, self.viewport().height() - height - 18), width, height)
+        # Top center, where the collapsed "?" badge sits — expanding must not
+        # send the mouse to the other end of the view to close it again.
+        bg_rect = QRectF((self.viewport().width() - width) / 2, 18, width, height)
         self._help_hit_rect = bg_rect  # click anywhere on the box to close
         painter.setPen(QPen(qcolor(LEGEND_TEXT, 60), 1))
         painter.setBrush(qcolor(LEGEND_BG, 190))