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/protocol/protocol.gd

@@ -11,7 +11,7 @@ class_name Protocol
 
 ## Protocol version — must match server PROTOCOL_VERSION in bridge/types.rs.
 ## Reject snapshots where version != this value.
-const PROTOCOL_VERSION: int = 4
+const PROTOCOL_VERSION: int = 5
 
 
 # -- Decode: bytes from server → GDScript types --------------------------------
@@ -94,6 +94,16 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 			if ni != null:
 				nearby_interactions.append(ni)
 
+	# v5: current_monologue (#414)
+	var current_monologue: Variant = null
+	var raw_monologue: Variant = raw.get("current_monologue")
+	if raw_monologue is Dictionary and raw_monologue.has("text"):
+		current_monologue = {
+			"id": str(raw_monologue.get("id", "")),
+			"text": str(raw_monologue["text"]),
+			"duration_seconds": float(raw_monologue.get("duration_seconds", 5.0)),
+		}
+
 	return {
 		"tick": tick,
 		"entities": entities,
@@ -103,6 +113,7 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 		"player_facing": player_facing,
 		"visible_tiles": visible_tiles,
 		"nearby_interactions": nearby_interactions,
+		"current_monologue": current_monologue,
 	}