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/src/content/spawn.rs

@@ -28,6 +28,7 @@ use crate::knowledge::types::{
     FactId, FactKnowledge, KnowledgeConfidence, KnowledgeSource, KnowledgeState, StableId,
 };
 use crate::npc;
+use crate::simulation::interaction::Interactable;
 use crate::simulation::movement::TilePosition;
 use crate::simulation::time::DayPhase;
 
@@ -89,6 +90,9 @@ fn spawn_npc(world: &mut World, profile: &types::NpcProfile, result: &mut SpawnR
     // Default position — will be overridden by routine system on first phase transition
     entity_commands.insert(TilePosition::new(0, 0, 0));
 
+    // Mark NPC as interactable for proximity-based verb detection (#413)
+    entity_commands.insert(Interactable);
+
     // Axis 1: Want
     if let Some(want) = &profile.want {
         if let Some(kind) = parse_want_kind(&want.primary) {