feat(plugins): ship SkillOpt-Sleep for Claude Code, Codex, and Copilot

Restructure into plugins/{claude-code,codex,copilot}/ — one engine, three thin
shells, all calling the shared plugins/run-sleep.sh -> python -m skillopt_sleep.

  - claude-code/: existing plugin moved here; runner delegates to the shared
    launcher (fixes repo-root resolution after the move).
  - codex/: ~/.codex/prompts/sleep.md custom prompt + ~/.agents/skills SKILL.md +
    install.sh + AGENTS.md hint — Codex's documented, stable extension surfaces.
  - copilot/: a stdlib-only MCP server (mcp_server.py) exposing sleep_* tools,
    plus mcp-config.example.json and a copilot-instructions snippet. Verified end
    to end (initialize -> tools/list -> tools/call returns real engine output).
  - plugins/README.md overview table; main README News + a dedicated SkillOpt-Sleep
    section; pyproject lists skillopt_sleep as a first-class package.

Decoupling emphasized throughout: open-source tool (skillopt_sleep/) with zero
dependency on the research package. 29 tests pass; all three shells resolve.

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

pyproject.toml

@@ -64,7 +64,9 @@ Repository = "https://github.com/microsoft/SkillOpt"
 Issues = "https://github.com/microsoft/SkillOpt/issues"
 
 [tool.setuptools.packages.find]
-include = ["skillopt*", "scripts*"]
+# skillopt* = the research package; skillopt_sleep = the open-source Sleep tool
+# (decoupled, zero dependency on the research code).
+include = ["skillopt", "skillopt.*", "skillopt_sleep", "skillopt_sleep.*", "scripts*"]
 
 [tool.ruff]
 line-length = 120