release(v4.8.6): Issue #17 item 4 - archive PR #51 reviews and bump the lockstep version

Merge-workspace review: round 1 (@518beda) claude agy grok PASS, codex
NOT PASS (finalize wait measured on the wall clock); fixed in 4c86107.
Round 2 delta (@4c86107) claude agy grok PASS; codex (24b21b9c, after
817d1650 closed deadline_timeout with no report) found R1 closed and no
new defect, but withheld PASS only because its sandbox could not bind
the suite's loopback broker. The same two-file suite run here at
4c86107: 278 passed. Full suite at 518beda on macOS / Python 3.9:
1711 passed / 1 failed / 38 skipped; the failure
(test_issue45_restore, herdr 0.9.3 cwd restore) also fails on main.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VCgu9Fa9iT7TbJUSzdq4Ff

.agents/skills/multi-agent-mux-stop/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: multi-agent-mux-stop
 description: "Stop an agent herdr session (claude, antigravity/agy) and update .mam/agent-sessions.yaml. Default stops gracefully and marks status=stopped with conversation preserved for resume. Does NOT delete on-disk conversation artifacts (jsonl/db) — those are preserved unless --purge-conversation is passed. Use when ending a work session, switching to a different one, or cleaning up before a fresh start."
-version: 4.8.5
+version: 4.8.6
 author: godopu
 license: MIT
 platforms: [linux, macos]