Log PPID+argv on refused register (agent_identity_conflict), alongside PID already shipped ed2902d

coder-mars-cc case 2026-08-24: chased a phantom launcher bug for 4 rounds because the identity-conflict alert only had cwd+PID (PID itself just shipped, was previously absent too). PPID would have named the offending session's parent on the FIRST alert instead of requiring live proc forensics that miss transient forks. Needs a shim change (llmmsg-srv-mcp.mjs, x-llmmsg-ppid/x-llmmsg-argv headers) across sh.git, not a hub-only fix. Scoped, not done.