refactor(prompt): 提示词去工具化 + WebUI 插件状态按运行期真相展示

## 1. 系统提示词/人格瘦身（工具用法搬去 tooldef 与 skill）

用户指出：默认系统提示词与 personal 里有大量本该属于 skill / 工具描述的内容。
核对属实，且已造成**真实故障**：提示词教模型用 cmd_run，而 cmd 外置按需后
工具根本不在清单里 ⇒ 模型第一轮调用不存在的工具，拿到「工具 cmd_run 不存在」。

改动：
- kernelmod/agent.defaultSystemPrompt：删掉 output_* 用法、工具分类清单、
  cmd_run/terminal/files 策略、并行策略、媒体工具清单、emoji 风格要求。
  只留：身份 + 「工具描述与技能索引会注入，先读再用」+「只依据工具返回值作答」。
- config.DefaultPersonaPrompt：只留身份/称呼/语气 + 版本以运行时快照为准
  （后者由 TestDefaultPersonaPromptHasNoVersionLiterals 钉住）。
- 命令与文件策略下沉到工具描述：cmd_run 补「完整 bash，支持管道/heredoc/重定向」，
  files_write 补「原子替换 + 覆盖受保护路径前留档」。
- 对话时序块自带语义说明（原先靠提示词解释，提示词一精简就丢语义）。
- 文档新增「提示词分层」章节（中英），写明归属判据与这次的反面教材。

## 2. WebUI：插件「启动状态」按运行期真相展示

旧实现只看内核 status 的 loaded 一个布尔，三种形态被混成同一个「未加载」：
auto_start=false 的按需待命（正常）、该起没起（异常）、plugin_stop 后的运行态停止。
用户看到一屏「未加载」以为插件全坏了。

- sdk.PluginRuntimeInfo 新增 AutoStart / RuntimeStopped；registry 从清单填充。
- pluginmgr /plugins 列表暴露 auto_start / runtime_stopped / builtin / tool_count。
- webui 新增 POST /plugins/<name>/start|stop（运行态，不动持久禁用清单）。
- dashboard 状态列改为五态：已禁用 / 进程丢失 / 已运行 / 按需待命 / 未运行，
  并额外标注「自启 / 按需」；按钮改为 启动/停止（运行态）与 禁用/启用（持久态）分列。
- 新增两条回归判据（引用 auto_start/runtime_stopped/alive 字段；startPlugin 走 /start）。

## 验收（本机实例实测）

- files 保持 auto_start=false（按需）；问 agent 写文件 → 它先 plugin_start cmd+files，
  再 files_write/files_read，内容校验一致；未用 shell 代替文件操作。
- WebUI 插件页截图确认：a2a/acp/agentcli 显示「已运行 自启」，
  ai_image 显示「按需待命 按需」+「启动」按钮。
- go test（config/agent core/plugin/pluginmgr/webui/sdk）全绿。

assets/docs/en/ARCHITECTURE.md

@@ -627,6 +627,37 @@ is relevant) and the timeline is taken newest-first within budget. Measured: wit
 budget, actual injection was still a few hundred characters.
 
 
+## Prompt layering (established 2026-10-20)
+
+The system prompt is **not** the place for tool usage instructions. Decide where a
+piece of text belongs by its lifetime and visibility:
+
+| Content | Belongs in | Why |
+|---|---|---|
+| Identity, how to address the user, tone, appearance | Persona (`personal/personal.md` or `core.agent.personal_prompt`) | Lives and dies with the persona; stable across plugins and channels |
+| One tool: when to use, parameter meaning, side effects, pitfalls | The tool `description` | **Travels with the tool**: if the plugin is absent or not started, the description is not in the list, so the model cannot misuse it |
+| Multi-step procedures, strategies, domain knowledge | Skills (`skill/<name>/SKILL.md`) | Progressive disclosure: the index is always present, the body is fetched on demand via `skill_info` |
+| Output-delivery rules, same-round parallelism, timeline semantics | Kernel runtime blocks (`buildSystemPrompt` / timeline header) | Generated from **actual** execution semantics; static copies drift from the implementation |
+
+**Anti-pattern (measured 2026-10-20)**: the default system prompt carried
+"cmd_run runs through a full bash…", "prefer files_write for writing files…",
+"spawn_child in parallel…". After those plugins were externalized and made
+on-demand, `cmd_run` was no longer in the tool list while the prompt still told
+the model to use it — the first turn called a nonexistent tool and only then
+learned "tool cmd_run not registered".
+
+**Rule of thumb**: a concrete tool name plus usage instructions in the prompt is
+almost always misplaced. The only exceptions are (1) tool names **injected at
+runtime** (e.g. `output_send__{channel}`, whose channel set changes per turn) and
+(2) statements about **kernel behaviour** rather than tool behaviour (e.g.
+"multiple calls in one round run in parallel by default").
+
+Likewise, a plugin's skill must ship **in the same package**: an
+`auto_start=false` plugin without a skill has its tools absent from the initial
+list, so the model never knows it exists and never starts it — equivalent to not
+being installed. hmapdev enforces this at packaging time
+(`autostart_skill_guard_test.go`).
+
 ## Configuration System
 
 `internal/config/registry.go` — ConfigRegistry