feat(simulation): complete interaction and monologue pipelines (#413, #414, #415)

Three fixes to make the gameplay loop functional end-to-end:

- Add Interactable component to NPC spawn so E-prompt detection works
- Build monologue trigger system (enter_location + time_idle) with
  MonologueBuffer/MonologueState components, wire through ObserverSnapshot
  as current_monologue field, decode on client and display via HUD
- Change PlayerAction::Interact from unit to struct variant carrying
  optional target_entity_id and verb fields

Bumps protocol version from 4 to 5. Regenerates MessagePack fixtures.
All 200 tests pass (170 unit + 30 integration).

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

server/tests/bridge_ipc.rs

@@ -33,7 +33,7 @@ fn snapshot_roundtrip_over_unix_socket() {
         let bridge = LocalBridge::accept(&server_path).expect("failed to accept");
 
         let snapshot = ObserverSnapshot {
-            version: 4,
+            version: PROTOCOL_VERSION,
             tick: 42,
             game_time: GameTime {
                 day: 0,
@@ -54,6 +54,7 @@ fn snapshot_roundtrip_over_unix_socket() {
             }],
             visible_tiles: vec![],
             nearby_interactions: vec![],
+            current_monologue: None,
         };
 
         bridge
@@ -116,7 +117,7 @@ fn input_roundtrip_over_unix_socket() {
         },
         PlayerInput {
             tick: 11,
-            action: PlayerAction::Interact,
+            action: PlayerAction::Interact { target_entity_id: None, verb: None },
         },
     ];
 
@@ -134,7 +135,7 @@ fn input_roundtrip_over_unix_socket() {
         _ => panic!("expected MoveNorth action"),
     }
     match &received_inputs[1].action {
-        PlayerAction::Interact => {}
+        PlayerAction::Interact { .. } => {}
         _ => panic!("expected Interact action"),
     }
 }