opencode QA

QA the opencode coding agent itself. This skill maps each QA need to a tested helper script and a deep reference. Every script ships a --self-test that asserts its scenario against the live machine, so the scripts are both the QA tools and their own regression checks.

Verified against opencode v1.15.13 (bun 1.3.12, macOS). Confirm the installed version with opencode --version; the surface is stable but always sanity check a flag with opencode <cmd> --help.