feat: 新增内置通用助手 / list built-in General Assistant (#216)

## 中文
新增通用助手的双语展示条目，主文件明确声明 system/repository，sidecar 使用
listing-only。市场展示内置状态，更新复用 Agent 仓库合并；客户端负责离线安装与默认手动多会话。


独立公开源仓库：[agent-general-assistant](https://github.com/desirecore/agent-general-assistant)，初始内容已通过
PR #1 合入 main。客户端实现：desirecore/desirecore#4814。

验证：i18n 与 catalog metadata 均 0 errors（105
条既有条目警告），翻译新鲜度与公开内容检查通过；客户端已从真实 main 生成种子，真实 bundle verification 通过。

## English
Add the bilingual General Assistant listing with explicit
system/repository policies and listing-only availability. The client
owns offline provisioning and manual multi-session defaults; updates use
the agent repository merge flow.

The public source repository is available on main. Client integration:
desirecore/desirecore#4814. i18n/catalog validation passed with 0 errors
and 105 existing warnings, alongside translation freshness and
publication checks. The real main-based seed and bundle verification
passed.

manifest.json

@@ -1,6 +1,6 @@
 {
   "name": "DesireCore Official Market",
-  "version": "1.5.10",
+  "version": "1.5.11",
   "schemaVersion": "1.1.0",
   "supportedLocales": [
     "zh-CN",
@@ -29,10 +29,10 @@
     "url": "https://github.com/desirecore/market.git"
   },
   "stats": {
-    "totalAgents": 7,
+    "totalAgents": 8,
     "totalTeams": 2,
     "totalSkills": 141,
-    "lastUpdated": "2026-10-05"
+    "lastUpdated": "2026-10-14"
   },
   "features": [
     "curated-index",