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/world.dungeon-activity.md

@@ -86,3 +86,7 @@
 本轮仍为 `PARTIAL`；完成三个地下城/活动方向的合同审计并登记，未修改实现。
 
 `PARTIAL`。当前端已经具备 `GC_DUNGEON` 目标点的主要 parser、坐标状态和与 40250 一致的 Manhattan/20 秒算法，也有结果窗口骨架；但 40250 的 compass `.mse` alarm 没有实际消费者，结果链缺少 live 回包时序证据，且 Boss、排行和具体副本 helper 是当前端本地 authority，不是 40250 Windows 客户端实现。本轮完成审计并记录，未修改实现。
+
+### 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：`dungeon_ranking_system.gd`, `endless_spire_dungeon_system.gd`, `flame_dungeon_razador_system.gd`, `spider_dungeon_system.gd`, `test_dungeon_ranking_parity.gd`, `test_endless_spire_dungeon_parity.gd`, `test_flame_dungeon_razador_parity.gd`, `test_spider_dungeon_key_parity.gd`, `test_spider_dungeon_parity.gd`, `world_boss_system.gd`。