chore: delete 106 unreachable *_system.gd and their parity tests

These files were loaded only by their own test_*_parity.gd and never by
the runtime (transitively checked, incl. client_phase_integration_system).
Removes 76 manifest implementation/evidence references across 18
contracts; contract docs get a note that conclusions based on them are
void. Live systems kept: chest, consumable, item_attr, metin_socket,
whisper_chat.

Full headless suite: no new failures (7 failing + 5 headless-hanging
render tests are identical before the deletion).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

audit/contracts/item.consumable-action.md

@@ -151,3 +151,7 @@
 `PARTIAL`。快捷栏增删/交换现在遵循请求→`GC_QUICKSLOT_*`→重建显示的权威时序，分页也已按 4 页取模；
 但快捷栏使用的统一入口、消耗品反馈闭环、真实回包 fixture、音效/sequence 和跨生命周期清理仍未闭合，
 因此不能把整个合同标记为 40250 等价。
+
+### 2026-09-22 死代码删除
+
+以下文件只被自身测试引用、运行时从不加载，已删除；本文中以它们为实现或证据的结论作废，相关行为需按 40250 源码单元重新移植：`item_split_system.gd`, `test_item_split_parity.gd`。