feat: default beamline state on login by role

Staff land in BeamLocation, users in SampleAlignment. One-shot on the
first status tick where the GUI owns the session and the beamline is
idle, so a running operation or a watch-only GUI is never disturbed.

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

src/aare/gui/main_window.py

@@ -173,6 +173,7 @@ class MainWindow(QMainWindow):
     _default_dock_split_done: bool = False
     _pre_watch_dock_state: QByteArray | None = None
     _pre_watch_visibility: list[tuple[QWidget, bool]] | None = None
+    _login_default_state_sent: bool = False
 
     def __init__(
         self,
@@ -2609,6 +2610,18 @@ class MainWindow(QMainWindow):
         self._apply_session_gate(getattr(getattr(s, "session", None), "session", None))
         self._apply_pgroup_gate(getattr(getattr(s, "session", None), "current_pgroup", None))
 
+        # Login default: staff start in BeamLocation, users in SampleAlignment.
+        # One-shot on the first status tick where this GUI owns the session and
+        # the beamline is idle — a busy beamline or watch-only GUI must never
+        # have its state yanked by someone merely logging in.
+        if not self._login_default_state_sent and self._session_operations_enabled and not s.busy:
+            self._login_default_state_sent = True
+            if self._decoded_token.staff:
+                if s.state != BeamlineStateEnum.BeamLocation:
+                    self.daq.beam_location()
+            elif s.state != BeamlineStateEnum.SampleAlignment:
+                self.daq.sample_alignment()
+
         # Default tab only on state TRANSITIONS — a manual tab choice
         # survives while the state stays put.
         new_beamline_state = getattr(s, "state", None)