0.16.1 — herdr stall recovery on output evidence

• herdr stall recovery rewritten on output evidence — live probing
  (2026-10-10) showed herdr 0.9.3's status watcher NEVER reports working
  for pi panes (state_change_seq frozen across live turns), so
  agent prompt --wait returned agent_prompt_stalled on healthy
  dispatches (every herdr delegation was affected; the child completed its
  work while the parent reported failure). The subagent module now snapshots
  an output-evidence baseline BEFORE submission (captureEvidenceStamp:
  report-file stamp + pane tail for read-only children) and, on a stall,
  waits on EVIDENCE for the remaining dispatch budget — a changed report-file
  stamp (delivery contract) or a changed-then-quiet pane tail (3 stable
  polls). Window exhaustion reports timeout semantics (pane interrupted,
  may-still-complete disclosure) — never a phantom hard stall. Verified live
  across all five agent types under 4-way concurrency, including a mid-turn
  Z.ai 429 recovery; 6 new regression tests (test/herdr-stalled.test.ts).