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/game_state.gd

@@ -22,6 +22,9 @@ var player_entity_id: int = 1
 # v4 fields (#404/#405)
 var nearby_interactions: Array = []  # [{entity_id, entity_type, distance, verbs: [{kind, label, priority, available}]}]
 
+# v5 fields (#414)
+var current_monologue: Variant = null  # {id, text, duration_seconds} or null
+
 func apply_snapshot(snapshot: Dictionary) -> void:
 	current_snapshot = snapshot
 
@@ -73,6 +76,12 @@ func apply_snapshot(snapshot: Dictionary) -> void:
 	else:
 		nearby_interactions = []
 
+	# v5: current_monologue (#414)
+	if snapshot.has("current_monologue") and snapshot.current_monologue is Dictionary:
+		current_monologue = snapshot.current_monologue
+	else:
+		current_monologue = null
+
 	# v2: visible_tiles with visibility sectors
 	# Derives visible_positions when not explicitly provided (real server mode)
 	if snapshot.has("visible_tiles") and snapshot.visible_tiles is Array and snapshot.visible_tiles.size() > 0: