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.

src/tools/registry.c

@@ -204,7 +204,12 @@ static const cst_tool_def_t TOOLS[] = {
      "Search earlier and current sessions for text.",
      {{"query", S, 1, "text to look for"},
       {"max_matches", I, 0, "stop after this many matches (default 20)"},
-      {"ignore_case", B, 0, "case-insensitive (default true)"}},
+      {"ignore_case", B, 0, "case-insensitive (default true)"},
+      {"max_bytes", I, 0,
+       "stop after this many bytes of transcripts (default 32 MB, newest "
+       "sessions first); 0 or unset means the default"},
+      {"max_seconds", I, 0,
+       "stop after this many seconds of searching (default 5)"}},
      CST_TP_READ, 0, cst_tool_session_search, NULL, NO_DYN, NO_META},
     {"device_info",
      "Where this agent is running: system and CPU count, workspace, sandbox, "