fix: correct OpenCode 2 command transport on current main

[ByBrawe]

Summary

• port the validated OpenCode 2 command transport fix from stale PR fix: correct OpenCode 2 command transport #97 onto current main
• send slash-command names through command, not id; OpenCode 2 reserves id for optional msg_... message IDs
• normalize /review to review in the host contract and idle-safe command runtime
• make the runtime adapter forward { sessionID, command, arguments? } and omit id
• add exact request-shape regressions at host-contract, runtime, and adapter/composition levels
• keep /compact deliberately outside the V2 command transport path and keep shell actions unsupported while the plugin context has no session.shell
• strengthen the real @opencode-ai/plugin@next adapter gate with a missing-command sentinel that only passes when the command field reaches the host correctly

Why a replacement PR

PR #97 contains the same final 8-file diff but was created from an older main and carries 14 historical commits. This branch starts directly from current main (e04973b...) and transplants only the final validated diff: 8 commits, 8 files, 0 commits behind.

Validation target

• current CI on Ubuntu/Windows
• V2 Lifecycle Contract
• real OpenCode 2 adapter gate using @opencode-ai/cli@next + @opencode-ai/plugin@next

Package version remains 0.5.28; no npm publish in this PR.

Supersedes #97.

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