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/social.party-guild-messenger.md

@@ -106,3 +106,7 @@
 ## Status
 
 `PARTIAL`。当前端的 native 社交协议和主要 UI 已有较完整骨架，组队、公会、好友和会徽 live 主路径大体接上 40250；但本地 party/guild skill/war/messenger/mark helper 仍把服务端权威逻辑复制成直接状态机，且真实权限拒绝、回包顺序、重连清理和独立会徽连接缺端到端证据。因此不能把现有 parity 测试通过等同于实现统一。本轮完成审计并记录，未修改实现代码。
+
+### 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：`guild_mark_uploader_system.gd`, `guild_skill_system.gd`, `guild_war_system.gd`, `messenger_system.gd`, `party_management_system.gd`, `test_guild_mark_uploader_parity.gd`, `test_guild_skill_parity.gd`, `test_guild_war_observer_arena_parity.gd`, `test_guild_war_parity.gd`, `test_messenger_parity.gd`, `test_party_management_parity.gd`, `test_privilege_empire_guild_parity.gd`。