Blood Brothers should start with objectives (#83030)

## About The Pull Request

Fixes #82064
Fixes a couple of different bugs with Blood Brothers.

- Delegates creating the objectives to the team rather than the ruleset,
so ones created via the traitor panel will also have objectives.
- Creates the objectives after the team has a member mind, so it doesn't
runtime when trying to give that mob the equipment needed to steal a
supermatter sliver.
- Creates the objectives before the first Blood Brother is assigned the
antag datum, so that they will correctly be given the starting
objectives.
- Check the maximum number of brothers that can be recruited when
deciding how many objectives to generate rather than the current number
of members (which would always be 1).

## Changelog

🆑
fix: Blood Brothers should spawn knowing what their objectives are.
fix: Teams of 3 Blood Brothers will once more have an additional
objective.
/🆑

code/controllers/subsystem/dynamic/dynamic_rulesets_roundstart.dm

@@ -135,10 +135,7 @@ GLOBAL_VAR_INIT(revolutionary_win, FALSE)
 
 /datum/dynamic_ruleset/roundstart/traitorbro/execute()
 	for (var/datum/mind/mind in assigned)
-		var/datum/team/brother_team/team = new
-		team.add_member(mind)
-		team.forge_brother_objectives()
-		mind.add_antag_datum(/datum/antagonist/brother, team)
+		new /datum/team/brother_team(mind)
 		GLOB.pre_setup_antags -= mind
 
 	return TRUE