feat(simulation): add NPC name masking with role labels and color index

Server-side infrastructure for information asymmetry in dialogue.
NPCs display role labels (Worker, Supervisor, Patron) instead of
real names until the player explicitly learns them via KG lookup.
NpcColorIndex (stable_id % 8) persists across name reveal.

ConversationEvent and DialogueResponseEvent carry display names +
color indices on the wire with serde(default) for compat.

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

server/src/test_world/rooms/shift_change.rs

@@ -24,10 +24,6 @@ use crate::simulation::path_follow::MovementSpeed;
 use crate::simulation::tier::ActiveSim;
 use crate::simulation::time::DayPhase;
 
-/// Room origin (top-left corner including walls).
-const ORIGIN_X: i32 = 64;
-const ORIGIN_Y: i32 = 78;
-
 /// Observer position for Shift Change tests (absolute).
 pub const OBSERVER_POS: TilePosition = TilePosition { x: 72, y: 90, z: 0 };