Assign standalone ghost roles on death

[XaineDev]

A custom role whose IsDead is true and that turns HideSettings off is now handed out when a player dies, from its lobby count and chance, the same way vanilla hands out Guardian Angel and Spirit Guide.

• It is rolled in the existing RoleManager.AssignRoleOnDeath prefix, before vanilla's specials. Roles with a configured GhostRole keep their current path.
• The role is set on every client through a new MiraRpc.SetGhostRole, not vanilla RpcSetRole.
• Freeplay assigns any enabled ghost role, so a lobby count above zero is enough to test one.
• Ghost roles still default to HideSettings = true; the doc comment now says what turning it off does.

Tested with au-influencer's Freeplay smoke test: a dead crewmate became the Influencer ghost role and the full post flow passed.