v0.9.7: a turn that cannot hang, a session list that reads nothing twice, and PDFs

- consent: on_permission / on_ask_user wait at most two / five minutes, and in
  the background (a phone off screen, a window that is gone) the answer is
  refused at once with a reason -- a dialog nobody can see blocked the worker
  for good, which is what "the app hangs while the agent works" looked like.
- finishTurn() no longer joins the thread it is called from; the event loop
  reaps the Turn instead.
- AndroidTools: the hop to the GUI thread pings first and gives up after 3 s
  instead of waiting forever on a busy GUI thread.
- the session list stopped reading every transcript: cst_agent_store_info()
  counts newlines in 64 KiB blocks (first_user only within the first 256 KiB),
  and AgentCore::sessions() reuses a row while (mtime, size) is unchanged.
- session_search gets a budget (max_bytes 32 MB, max_seconds 5 s), skips lines
  over 64 KiB, and says when the budget stopped the walk.
- the header shows the phase ("shell: make -j8"), so a long turn no longer
  looks like a stuck one.
- md_to_pdf: the front end's own Qt tool (owner app:qt, every platform):
  markdown or a workspace .md/.html becomes an A4 PDF with 15 mm margins,
  paginated by hand, written into the workspace and delivered as a file card.
  No PrintSupport, so the phone gets it too.
- --uitest runs md_to_pdf through the registry with Chinese text and checks the
  bytes are a PDF; app/CMakeLists.txt no longer drops src/web_md.c from the
  standalone engine build, which the window needs to render markdown.

Version 0.9.7.

README.md

@@ -325,7 +325,8 @@ cst-agent --headless --prompt 'List files'
 | `task` | 子 agent | 把独立任务交给子 agent（`general` / `explore` / `plan` / 自定义角色），只返回最终报告 |
 | `deliver_file` | 交付 | 把工作区里的成品文件复制进会话库并交给用户（任意字节，≤64 MB）：前端画成文件卡，可打开 / 分享；带 `for_user` 标记，永不进模型上下文 |
 | `md_to_html` | 文档 | 把 markdown（文本或工作区 `.md`）渲染成一份自包含 HTML 文档写进工作区并交付成文件卡：utf-8、标题、内联样式，无脚本无外链 |
-| `session_search` | 读 | 在过去和当前的所有会话转录里搜子串，给会话 id、条数、标题和匹配行（行号 + 角色 + 上下文） |
+| `md_to_pdf` | 文档 | 图形前端（桌面 / APK）自带：把 markdown 或工作区 `.md` / `.html` 排成 A4 PDF（15 mm 边距，自动分页）写进工作区并交付成文件卡；不需要 Qt PrintSupport，手机上也能出 |
+| `session_search` | 读 | 在过去和当前的所有会话转录里搜子串，给会话 id、条数、标题和匹配行（行号 + 角色 + 上下文）；有预算：`max_bytes`（默认 32 MB）、`max_seconds`（默认 5 s），超 64 KiB 的单行跳过，被预算截断时结果里写清楚 |
 | `device_info` | 读 | 报告运行环境：系统 / 架构 / CPU 数、工作区、沙箱、模型与审批模式、config / temp / 程序目录、pid（审批策略名 `device`） |
 
 插件工具和 MCP 工具（`mcp__<server>__<tool>`）在运行时注册，和内置工具走同一套审批与 `/tools` 开关。