feat(events): add booking_occupancy on event JSON for studio grid

Expose free|pending|confirmed so commercial calendar can aggregate
slots by occupancy without N GET /bookings calls.

src/handlers/handler_events.erl

@@ -339,10 +339,14 @@ parse_datetime_binary(Str) ->
   Dt.
 
 occurrence_to_json(Master, Occurrence) ->
+  %% Virtual row: occupancy by master event id (materialized instances use event_to_json).
   #{
     master_id  => Master#event.id,
     start_time => handler_utils:datetime_to_iso8601(Occurrence),
     duration   => Master#event.duration,
     title      => Master#event.title,
-    is_virtual => true
-  }.
+    is_virtual => true,
+    specialist_id => Master#event.specialist_id,
+    calendar_id => Master#event.calendar_id,
+    booking_occupancy => handler_utils:booking_occupancy(Master)
+  }.

src/handlers/handler_utils.erl

@@ -19,6 +19,7 @@
   parse_datetime/1,
   datetime_to_iso8601/1,
   event_to_json/1,
+  booking_occupancy/1,
   user_to_json/1,
   review_to_json/1,
   review_to_json/2,
@@ -300,6 +301,8 @@ audit_reason(#{<<"reason">> := R}) when is_binary(R) -> R;
 audit_reason(_) -> <<>>.
 
 %% @doc Преобразует #event{} в JSON-карту.
+%% Добавляет booking_occupancy: free | pending | confirmed
+%% (confirmed > pending > free; cancelled/expired и past-pending → не занятость).
 -spec event_to_json(#event{}) -> map().
 event_to_json(Event) ->
   LocationJson = case Event#event.location of
@@ -337,9 +340,29 @@ event_to_json(Event) ->
     attachments     => Event#event.attachments,
     edit_history    => Event#event.edit_history,
     created_at      => datetime_to_iso8601(Event#event.created_at),
-    updated_at      => datetime_to_iso8601(Event#event.updated_at)
+    updated_at      => datetime_to_iso8601(Event#event.updated_at),
+    booking_occupancy => booking_occupancy(Event)
   }.
 
+%% @doc Активная занятость слота для сетки commercial (Studio aggregate).
+-spec booking_occupancy(#event{}) -> free | pending | confirmed.
+booking_occupancy(#event{id = EventId, start_time = Start}) ->
+  {ok, Bookings} = core_booking:list_by_event(EventId),
+  Now = calendar:universal_time(),
+  lists:foldl(
+    fun(#booking{status = confirmed}, _Acc) ->
+          confirmed;
+       (#booking{status = pending}, Acc) ->
+          case Start > Now of
+            true when Acc =/= confirmed -> pending;
+            _ -> Acc
+          end;
+       (_, Acc) ->
+          Acc
+    end,
+    free,
+    Bookings).
+
 %% @doc Преобразует #user{} в JSON-карту.
 -spec user_to_json(#user{}) -> map().
 user_to_json(User) ->