refactor(i18n): fragments 为唯一源，主包改为生成物

- 一次性回灌：主包最新内容（含 565 个未同步键）全量写回 6 个 fragment 文件，fragments 成为完整唯一源；新增 core fragment（common/docs/home 等 9 个此前仅存在于主包的命名空间）
- merge-i18n-fragments.mjs 改为从零重建主包（不再以主包为基础），重建结果与原主包语义零差异
- 主包 messages/{zh-CN,en}.json 移出跟踪并加入 .gitignore
- 生成接入入口：predev/prebuild/prebuild:embed/precheck:i18n 钩子 + Makefile code-check 与 checks.sh vitest 前置生成
- 修复既有漂移：configVersions.title 现以 fragments（Config versions）为准

frontend/messages/fragments/security.en.json

@@ -181,7 +181,6 @@
     "deleting": "Deleting...",
     "confirmDelete": "Delete",
     "operationFailed": "Operation failed",
-    "autoConfigMustBeObject": "Automatic configuration must be a JSON object.",
     "types": {
       "manual": "Manual",
       "automatic": "Automatic",
@@ -274,7 +273,8 @@
       "deleteDesc": "Remove {ip} from IP group “{name}”?",
       "deleting": "Deleting...",
       "confirmDelete": "Delete"
-    }
+    },
+    "autoConfigMustBeObject": "Automatic configuration must be a JSON object."
   },
   "rateLimits": {
     "title": "Rate limits",