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/tests/serialization.rs

@@ -318,7 +318,7 @@ fn protocol_version_constant_matches_snapshot() {
     let snapshot = test_snapshot(0, vec![]);
     assert_eq!(snapshot.version, PROTOCOL_VERSION);
     assert_eq!(
-        PROTOCOL_VERSION, 11,
+        PROTOCOL_VERSION, 12,
         "bump this assertion when protocol version changes"
     );
 }