test(simulation): sprint 10 — replay loading, content scaling, serialization v9, observer tests

#483: Replay loading in test-client — JSONL file loading, tick-scheduled
PlayerInput sending, 13 unit tests, 3 sample replay files.
#500: Content scaling test — baseline + extra NPC comparative, tick budget
assertion (D-026), determinism check across content packs.
#514: Serialization tests for protocol v9 — blocked_entities roundtrip,
backward compat (v5→v9, v8→v9), regenerated msgpack fixtures.
Observer perception tests for confrontation + walk-away mechanics.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/tests/gen_fixtures.rs

@@ -35,6 +35,7 @@ fn fixture_snapshot(tick: u64, entities: Vec<VisibleEntity>) -> ObserverSnapshot
         current_monologue: None,
         pending_recognitions: vec![],
         dialogue_response: None,
+        blocked_entities: vec![],
     }
 }
 
@@ -204,6 +205,7 @@ fn generate_msgpack_fixtures() {
         current_monologue: None,
         pending_recognitions: vec![],
         dialogue_response: None,
+        blocked_entities: vec![],
     };
     write_fixture(
         "snapshot_v2_full",