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>

client/scripts/autoloads/sim_bridge.gd

@@ -309,6 +309,15 @@ func _test_snapshot() -> Dictionary:
 			],
 		})
 
+	# v5: monologue on first tick (#414)
+	var monologue: Variant = null
+	if _test_tick == 1:
+		monologue = {
+			"id": "test_enter_001",
+			"text": "Sova Transit District. Population twelve thousand and change.",
+			"duration_seconds": 5.0,
+		}
+
 	return {
 		"tick": _test_tick,
 		"version": Protocol.PROTOCOL_VERSION,
@@ -324,6 +333,7 @@ func _test_snapshot() -> Dictionary:
 		"visible_tiles": _test_visible_tiles(),
 		"visible_positions": _test_visible_positions(),
 		"nearby_interactions": nearby,
+		"current_monologue": monologue,
 	}
 
 # Generate a small test room: 8x6 room with walls, a door, and floor