fix: grey out whole state strip while beamline is busy

Busy now empties the available-target set exactly like Moving, so no
entry looks clickable and no transition can be posted mid-operation
(same guard the status-bar menu already had). The current/pending
entry keeps its highlight as orientation.

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

src/aare/gui/panels/beamline_state_panel.py

@@ -132,6 +132,7 @@ class BeamlineStatePanel(QFrame):
         self._current_state: BeamlineStateEnum | None = None
         self._hovered_state: BeamlineStateEnum | None = None
         self._pending_target_state: BeamlineStateEnum | None = None
+        self._busy = False
 
         # After 3 s of hovering an unavailable state, explain which states
         # it can be reached from.
@@ -238,7 +239,9 @@ class BeamlineStatePanel(QFrame):
 
     def _available_targets(self) -> frozenset[BeamlineStateEnum]:
         current = self._current_state
-        if current is None or current == BeamlineStateEnum.Moving:
+        # Busy greys the whole strip like Moving does: a transition posted
+        # mid-operation would clobber it (same guard as the status-bar menu).
+        if self._busy or current is None or current == BeamlineStateEnum.Moving:
             return frozenset()
         # Reachable in one step: the route graph plus the status-bar
         # shortcut transitions.
@@ -399,4 +402,7 @@ class BeamlineStatePanel(QFrame):
         self._apply_highlight()
 
     def update_daq_status(self, status: DAQStatusModel) -> None:
+        self._busy = bool(status.busy)
+        # set_current_state re-applies the highlight, so a busy flip
+        # restyles the strip on the same tick even if the state held.
         self.set_current_state(status.state)