Gate-view pos-1 lockout: thread the acting ?seat through the GATE VIEW nav — TDD

The GATE VIEW buttons (navbar + room.html lapsed-cost) linked to room_gate
with no ?seat, so _viewer_current_slot fell back to owned[0] (pos 1). On the
gate view a CARTE multi-seat gamer acting at pos 2+ saw pos 1 wrongly flagged
me-current AND href-less — the one circle you could never switch back to.

Fix (option a): _role_select_context + _gate_context now both expose
current_slot; both GATE VIEW buttons append ?seat={{ current_slot }} on
page-room. The gate view's current now matches the table → pos 1 becomes
me-also (switch href) when acting elsewhere, the occupied seat correctly
carries no href. _gate_context computes current_slot once and reuses it for
gate_positions.

3 ITs in CarteTrayFollowsSelectedSeatTest (button carries acting seat;
default targets lowest owned; gate page re-carries seat + pos 1 is me-also).
911 epic+gameboard ITs green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/apps/epic/views.py

@@ -336,6 +336,7 @@ def _expire_lapsed_seats(room):
 
 def _gate_context(room, user, seat_param=None):
     _expire_reserved_slots(room)
+    current_slot = _viewer_current_slot(room, user, seat_param)
     slots = room.gate_slots.order_by("slot_number")
     pending_slot = slots.filter(status=GateSlot.RESERVED).first()
     user_reserved_slot = None
@@ -390,9 +391,10 @@ def _gate_context(room, user, seat_param=None):
         "carte_slots_claimed": carte_slots_claimed,
         "carte_nvm_slot_number": carte_nvm_slot_number,
         "carte_next_slot_number": carte_next_slot_number,
-        "gate_positions": _gate_positions(
-            room, user, _viewer_current_slot(room, user, seat_param)
-        ),
+        # Acting seat — exposed so the gate page's own GATE VIEW re-click
+        # re-carries ?seat (keeps the seat-switch context across reloads).
+        "current_slot": current_slot,
+        "gate_positions": _gate_positions(room, user, current_slot),
         "starter_roles": [],
     }
 
@@ -486,6 +488,11 @@ def _role_select_context(room, user, seat_param=None):
             role_select_deck_id = seat_w_deck.deck_variant_id
     ctx = {
         "card_stack_state": card_stack_state,
+        # The viewer's acting seat (?seat slot, else lowest owned). Threaded
+        # onto the GATE VIEW nav so the gate view's current matches the table
+        # — without it the gate view falls back to owned[0] (pos 1), locking
+        # pos 1 as a never-switchable me-current circle.
+        "current_slot": current_slot,
         "equipped_deck_id": role_select_deck_id,
         "starter_roles": starter_roles,
         "assigned_seats": assigned_seats,