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/tests/gen_fixtures.rs

@@ -18,7 +18,7 @@ fn write_fixture(name: &str, bytes: &[u8]) {
 /// Helper to create a minimal v2 snapshot for fixtures
 fn fixture_snapshot(tick: u64, entities: Vec<VisibleEntity>) -> ObserverSnapshot {
     ObserverSnapshot {
-        version: 4,
+        version: PROTOCOL_VERSION,
         tick,
         game_time: GameTime {
             day: 0,
@@ -30,6 +30,7 @@ fn fixture_snapshot(tick: u64, entities: Vec<VisibleEntity>) -> ObserverSnapshot
         entities,
         visible_tiles: vec![],
         nearby_interactions: vec![],
+        current_monologue: None,
     }
 }
 
@@ -151,7 +152,7 @@ fn generate_msgpack_fixtures() {
 
     // v2 snapshot with visible_tiles and game_time populated
     let snapshot_v2_full = ObserverSnapshot {
-        version: 4,
+        version: PROTOCOL_VERSION,
         tick: 500,
         game_time: GameTime {
             day: 1,
@@ -194,6 +195,7 @@ fn generate_msgpack_fixtures() {
             },
         ],
         nearby_interactions: vec![],
+        current_monologue: None,
     };
     write_fixture(
         "snapshot_v2_full",
@@ -208,7 +210,7 @@ fn generate_msgpack_fixtures() {
         },
         PlayerInput {
             tick: 0,
-            action: PlayerAction::Interact,
+            action: PlayerAction::Interact { target_entity_id: None, verb: None },
         },
     ];
     write_fixture(