feat(pi-subagents): 重新启用子 Agent 并使用独立的子 Agent 提示词

- 根包恢复 file:./pi-subagents 依赖与 extensions/subagents.ts 加载
  （排在 permission-system 之后、Tool Search 之前），并刷新根锁文件；
  Agent / get_subagent_result / steer_subagent 权限设为 allow，
  子 Agent 内的实际操作仍逐个经权限系统并转发主会话。
- 新增 config/prompt/subagent/：执行者角色 preamble 与组合包自带的
  general-purpose / Explore / Plan 定义（替换上游内置，去掉 bash find
  冲突规则与写死的 Haiku 模型）。
- pi-subagents 新增 basePrompt / bundledAgentsDir / excludedExtensionPaths
  选项：子 Agent 不再嵌入父会话提示词，身份标记置于开头；子会话排除
  pi-ask-user。未传选项时保持上游行为。
- system-prompt.ts：customPrompt 自带开场白时不再覆盖（修复子 Agent 角色
  与 <active_agent> 身份被抹掉）；仅凭 customPrompt 上的 <active_agent>
  识别子会话，routing 规则支持 scope，sections 支持 subagentExclude
  （子会话去掉 memory_policy 与 chrome_profile_bridge）。
- pi-hermes-memory：子会话只读，记忆/skill 写入工具返回错误，后台整理、
  纠错检测、会话 flush 与索引写入全部跳过。

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

config/prompt/routing.jsonc

@@ -3,6 +3,8 @@
   // <tool_routing> section. A rule is included when every tool in "whenAll"
   // and at least one tool in "whenAny" is active; a rule with neither is
   // always included. Rules render in file order as "- <text>".
+  // Optional "scope": "main" | "subagent" restricts a rule to that session
+  // audience (main session vs pi-subagents child); absent means both.
   "version": 1,
   "rules": [
     {
@@ -27,8 +29,14 @@
     },
     {
       "whenAny": ["ssh_connect"],
+      "scope": "main",
       "text": "Use ssh_connect only when the user explicitly names an imported host as part of a concrete remote task. Call it as a separate step and wait for success before calling other ssh_* tools; never infer or substitute a different host."
     },
+    {
+      "whenAny": ["ssh_connect"],
+      "scope": "subagent",
+      "text": "Use ssh_connect only when the delegated task explicitly names an imported host as part of a concrete remote task. Call it as a separate step and wait for success before calling other ssh_* tools; never infer or substitute a different host."
+    },
     {
       "whenAny": ["ssh_cd"],
       "text": "Treat ssh_cd as a reviewed persistent workspace transition: call it as a separate step and wait for success before issuing ssh_bash or relative ssh_read/ssh_write/ssh_edit/ssh_find/ssh_grep calls that depend on the new remote cwd. Use cd inside ssh_bash only for an intentionally temporary, command-local directory change."