Adds an opt-in 'youngPlayerSystem.enabled' server setting (default true) that, when set to false, disables the Young player system server-wide:
- Account.Young and PlayerMobile.Young getters short-circuit to false.
- New characters no longer receive Young status or a NewPlayerTicket.
- All downstream Young checks (notoriety beneficial-action restriction, CheckYoungProtection, stealing penalties, YoungDeathTeleport, death-item movement, poison immunity, '(Young)' name suffix, CanLogout, renounce-young keyword/gump, BaseCreature.OnDeath fame penalty, OnLogin time-remaining message) become inert.
Setters are intentionally left untouched so serialized account/player flags round-trip cleanly when the setting is later re-enabled.
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