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/golden/proof_room_tick_10.json

@@ -73,7 +73,7 @@
   "scan_events": [],
   "sound_events": [],
   "tick": 8,
-  "version": 14,
+  "version": 15,
   "visible_tiles": [
     {
       "tile_kind": "Wall",