v0.6.1: Stopping a session now stops what it started

• k in the table stops the whole process tree, as agent-ps stop already
  did. It was reading the agent rows rather than the process table, so a
  session's MCP servers and helpers were left orphaned.
• A stop is no longer reported as failed when it worked. SIGKILL is delivered
  after os.kill returns, and the check ran before the kernel had finished.
• When something does survive, the message names the PIDs instead of only
  counting them.