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/main.rs

@@ -14,7 +14,8 @@ use settled_reach_server::npc::{
     Want, WantKind,
 };
 use settled_reach_server::perception::vision_cone::Facing;
-use settled_reach_server::simulation::interaction::NearbyInteractionBuffer;
+use settled_reach_server::simulation::interaction::{Interactable, NearbyInteractionBuffer};
+use settled_reach_server::simulation::monologue::{MonologueBuffer, MonologueState};
 use settled_reach_server::simulation::movement::{PlayerCharacter, TilePosition, WalkabilityMap};
 use settled_reach_server::simulation::path_follow::MovementSpeed;
 use settled_reach_server::simulation::time::DayPhase;
@@ -50,6 +51,7 @@ fn main() {
     app.add_plugins(BridgePlugin);
     app.add_plugins(KnowledgePlugin);
     app.add_plugins(NpcPlugin);
+    app.add_plugins(settled_reach_server::content::ContentPlugin);
     app.insert_resource(BridgeResource::new(bridge));
     app.insert_resource(WalkabilityMap::new(32, 32, 1));
 
@@ -70,6 +72,8 @@ fn main() {
             Facing::default(),
             KnowledgeGraph::new(),
             NearbyInteractionBuffer::default(),
+            MonologueState::default(),
+            MonologueBuffer::default(),
         ))
         .id();
     registry.register(player);
@@ -79,6 +83,7 @@ fn main() {
         .world_mut()
         .spawn((
             Npc,
+            Interactable,
             TilePosition::new(16, 13, 0),
             Want {
                 primary: WantKind::Wealth,
@@ -125,6 +130,7 @@ fn main() {
         .world_mut()
         .spawn((
             Npc,
+            Interactable,
             TilePosition::new(14, 18, 0),
             Want {
                 primary: WantKind::Knowledge,
@@ -161,6 +167,7 @@ fn main() {
         .world_mut()
         .spawn((
             Npc,
+            Interactable,
             TilePosition::new(18, 14, 0),
             Want {
                 primary: WantKind::Safety,