feat(sleep): add OpenCode CLI backend for plain replay - #218

Part of #56

Implemented

• Added OpenCode as a SkillOpt Sleep backend (--backend opencode) and wired it through the CLI, config, backend factory, and sleep cycle.
• Added plain replay through the installed OpenCode CLI, using the user's existing OpenCode login, provider environment variables, and file-based global configuration.
• Plain replay runs from a temporary working directory with project configuration, tool use, external plugins, and configured MCP servers disabled.
• Added JSONL response parsing. Calls stop before model execution if SkillOpt cannot verify that all configured MCP servers are disabled, and failed calls are not cached.
• Added focused tests, opt-in real-CLI smoke tests, documentation, and a changelog entry.

Validation

• Focused automated tests: 61 passed, 2 skipped. The two opt-in live tests are skipped by default.
• Live tests used OpenCode 1.18.15 with its built-in opencode provider and the free opencode/deepseek-v4-flash-free model. No SkillOpt-specific provider credentials were configured.
• The real plain-replay and cycle-level smoke tests passed on Windows.
• The same tests passed on Ubuntu 26.04 under WSL2 with Python 3.12.13.
• Wheel and sdist builds passed, and the installed wheel passed a CLI smoke test.
• Documentation built successfully with python -m mkdocs build --strict.
• Full Windows test run: 932 passed, 17 skipped, 37 failed. The 37 failures were outside the OpenCode tests and were concentrated in existing Windows-specific Devin, Superpowers, Pi, and Cursor tests.

Scope and follow-ups

This PR covers the core OpenCode CLI backend and plain replay.

Separate follow-up work will cover:

• OpenCode transcript harvesting and --source opencode
• Structured tool replay with explicit opt-in
• A native OpenCode Sleep plugin or command
• Optional OpenCode support in the Copilot and Devin Sleep MCP integrations
• A documented OpenCode version range and improved error reporting