fix(simulation): PR #68 review — version bump, tracing warns, test coverage

- Bump PROTOCOL_VERSION 14 → 15 for save_result field addition
- Add tracing::warn on SaveLoadPending command overwrite (double-tap F5)
- Add tracing::warn on KnowledgeGraph::new() fallback during save
- Fix misleading WouldBlock comment in tcp.rs
- Document SimSpacePressure.active_count pre-eviction timing
- Document entity-based eviction tie-breaking non-determinism
- Add ScopePinned eviction survival regression test
- Regenerate msgpack fixtures for protocol v15

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

server/tests/serialization.rs

@@ -346,7 +346,7 @@ fn protocol_version_constant_matches_snapshot() {
     let snapshot = test_snapshot(0, vec![]);
     assert_eq!(snapshot.version, PROTOCOL_VERSION);
     assert_eq!(
-        PROTOCOL_VERSION, 14,
+        PROTOCOL_VERSION, 15,
         "bump this assertion when protocol version changes"
     );
 }