v1.15.1 — a stopped server exits even if its logout hangs; `activity tasks` mentions unreadable tasks beside readable ones

Corrections to 1.15.0, from an independent review on 2026-09-15.

A stopped server exits within five seconds, even if its logout hangs. 1.15.0 made the server log out when
Claude Code stops it: the first stop signal ignored further stop signals and ran the atexit logout. The logout
had no time limit. pyVmomi connects with httpConnectionTimeout=None, so a logout to a vCenter that stopped
answering, or one waiting on the SOAP connection lock a tool call held when the signal arrived, kept the server
running and deaf to every further stop signal until something sent SIGKILL. Before 1.15.0, SIGTERM at least
ended it.

• The logout now runs on a worker thread and gets 5 seconds. If it has not finished, the server writes one line
  to stderr without blocking (a full pipe cannot hold the exit) and exits with 128 + signal anyway; vCenter or
  ESXi ends that session when it idles out.
• New test: the real server with stdin held open, an atexit callback that blocks for ten minutes, then SIGINT
  and SIGTERM. The server must exit within 15 seconds and say it gave up on the logout. It failed on 1.15.0.
• Lab, on this code: eight conversations against vCenter 8.0.3 and ESXi 8.0.3, including active_tasks on both,
  left no session behind; afterwards both session lists held only the counting call's own session.

activity tasks mentions unreadable tasks beside readable ones. 1.15.0 printed unreadable_note only when
no task could be read. With some tasks readable it printed their table and nothing else, which reads as "these
are all the tasks". The note is now printed under the table too. The MCP result was already right.

• references/cli-reference.md said --target defaults to the first target; it now names default_target.