Add boss team match playstyle rule

When enabled, the sticky boss banner shows the next boss's team size
as a hint for players who voluntarily match the boss's party count.
Handles variant boss teams by using the auto-detected starter variant.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/app/seeds/inject_test_data.py

@@ -149,6 +149,7 @@ DEFAULT_RULES = {
     "levelCaps": False,
     "hardcoreMode": False,
     "setModeOnly": False,
+    "bossTeamMatch": False,
     "egglocke": False,
     "wonderlocke": False,
     "randomizer": False,