feat(task): add --resume-id <threadId> option for explicit thread resumption

[hirotomoyamada]

Summary

• Add --resume-id <threadId> value option to the task command for resuming a specific thread by ID
• Existing --resume (boolean) and --resume-last behavior is unchanged

Using a separate --resume-id flag instead of overloading --resume preserves backward compatibility with the rescue command routing that uses bare --resume as a boolean continue signal.

Closes #230

Changes

• handleTask(): add --resume-id as a value option, extract resumeId
• buildTaskRequest(): pass resumeId through the request object
• executeTaskRun(): use resumeId directly when provided, fall back to resolveLatestTrackedTaskThread() for --resume-last
• Usage text updated to show --resume-id <threadId>

Test plan

• task --resume-id <valid-threadId> "prompt" resumes the specified thread
• task --resume "prompt" still works as boolean resume (unchanged)
• task --resume-last "prompt" still resumes the latest thread (unchanged)
• task --resume-id <id> --fresh throws an error
• task --resume-id <id> --background works correctly
• task "prompt" without resume flags creates a new thread (unchanged)

[chatgpt-codex-connector]

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[yaronhuang]

+1 from a parallel use case — happy to see this PR exists.

We're building a Claude Code subagent (worker-codex) that wraps the codex-companion task runtime so multiple parallel teammates can each maintain their own Codex thread. Without --resume-id, our workaround is to override CODEX_COMPANION_SESSION_ID per teammate and emit a ===worker-codex thread: <uuid>=== sentinel as the shim's first stdout line, so the wrapper agent can recover the UUID from its own conversation history and pass it back. It works, but it's a brittle dance: env-var override is undocumented surface, and the sentinel can be lost to transcript truncation or wrapper drift.

--resume-id <threadId> is the right primitive — it lets the wrapper track and pass the thread ID explicitly without env-var hacks. The implementation here looks clean (preserves backward-compat with --resume-last, threads resumeId straight through buildTaskRequest() → executeTaskRun()).

Happy to test the branch locally against our parallel-teammate workflow if useful for review evidence. Tracking on our side: yaronhuang/kai#360.