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.

app/README.md

@@ -296,6 +296,26 @@ and two buttons.
   buttons, clicks Open (the header must say `opened report.md`), clicks Share
   and checks a name the session does not own is refused.
 
+### Making one: `md_to_pdf`
+
+The front end registers a tool of its own for this (`app/src/core/PdfTools.cpp`,
+owner `app:qt`, `platforms = NULL` so every platform the window runs on gets
+it): markdown, or a workspace `.md`/`.html` file, becomes an A4 PDF with 15 mm
+margins in the workspace, and goes through the same
+`cst_attach_import_artifact()` path as `deliver_file` -- so it arrives as a
+file card the person can open, print or share, and its bytes never enter a
+request. The markdown is rendered by the engine (`cst_web_md_document()`, the
+same renderer the WebUI and `md_to_html` use) and Qt lays the HTML out
+(`QTextDocument` + `QPdfWriter`, both QtGui); pagination is written here,
+page rect by page rect, because `QPrinter`/PrintSupport is desktop-only and a
+phone has no print subsystem. The tool runs on the turn's worker thread, and
+`--uitest` runs it through the registry and checks the file starts with
+`%PDF-`.
+
+The card row on the phone is the same one a picture uses: the store keeps the
+PDF next to the session, the image provider refuses it (it is not an image),
+and the file card carries it.
+
 ## Transcript, tool calls, streaming text
 
 - A tool call is a card of its own, and the call **id** is what pairs it with