feat(specialists): owner is non-deletable specialist on commercial create

Bootstrap calendar_specialist for owner (active); DELETE owner → 403;
toggle via status. Fixes solo assign-to-slot. Refs EventHub/EventHubBack#66

src/logic/logic_calendar_specialist.erl

@@ -5,7 +5,7 @@
 -module(logic_calendar_specialist).
 -include("records.hrl").
 
--export([list/2, add/5, update/4, remove/3, to_json/1]).
+-export([list/2, add/5, update/4, remove/3, to_json/1, ensure_owner_specialist/1]).
 
 -spec list(ActorId :: binary(), CalendarId :: binary()) ->
   {ok, [#calendar_specialist{}]} | {error, not_found | access_denied}.
@@ -47,14 +47,34 @@ update(OwnerId, CalendarId, UserId, Updates) ->
   end.
 
 -spec remove(OwnerId :: binary(), CalendarId :: binary(), UserId :: binary()) ->
-  ok | {error, not_found | access_denied | not_commercial | term()}.
+  ok | {error, not_found | access_denied | not_commercial |
+        owner_specialist_protected | term()}.
 remove(OwnerId, CalendarId, UserId) ->
   case require_owner_commercial(OwnerId, CalendarId) of
+    {ok, #calendar{owner_id = CalOwnerId}} when UserId =:= CalOwnerId ->
+      {error, owner_specialist_protected};
     {ok, _} ->
       core_calendar_specialist:delete(CalendarId, UserId);
     Error -> Error
   end.
 
+%% @doc Idempotent: commercial calendar always has a specialist row for owner.
+%% Default status=active; name from nickname (else email). No-op if already present.
+-spec ensure_owner_specialist(#calendar{}) -> ok | {error, term()}.
+ensure_owner_specialist(#calendar{id = CalId, owner_id = OwnerId, type = commercial}) ->
+  case core_calendar_specialist:get_by_calendar_and_user(CalId, OwnerId) of
+    {ok, _} ->
+      ok;
+    {error, not_found} ->
+      case core_calendar_specialist:create(CalId, OwnerId, owner_display_name(OwnerId), []) of
+        {ok, _} -> ok;
+        {error, already_exists} -> ok;
+        {error, _} = Err -> Err
+      end
+  end;
+ensure_owner_specialist(_) ->
+  ok.
+
 -spec to_json(#calendar_specialist{}) -> map().
 to_json(S) ->
   #{
@@ -82,3 +102,13 @@ require_owner_commercial(OwnerId, CalendarId) ->
       {error, access_denied};
     Error -> Error
   end.
+
+owner_display_name(OwnerId) ->
+  case core_user:get_by_id(OwnerId) of
+    {ok, #user{nickname = Nick}} when is_binary(Nick), Nick =/= <<>> ->
+      Nick;
+    {ok, #user{email = Email}} when is_binary(Email), Email =/= <<>> ->
+      Email;
+    _ ->
+      <<"Owner">>
+  end.