fix: flush large activity output

[roodboi]

Summary

• await completion of stdout writes for activity/history responses larger than the buffered console window
• preserve existing console behavior for normal-sized command output
• add a subprocess regression covering output above 128 KiB

Verification

• ./scripts/test-safe.sh src/util/cli-output.test.ts src/ai-cli.test.ts (18 pass)
• bun run type-check
• bun run check
• git diff --check
• real machine-local source dogfood: aggregate activity emitted 184,632 bytes and parsed as version 2 JSON with 12 feeds

Follow-up for the published aggregate activity compatibility gate discovered during HACK-932 dogfood.

---

^{Need help on this PR? Tag /codesmith with what you need. Autofix is disabled.}

[linear-code]

HACK-932

[roodboi]

@codex review exact head 4414e2f

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. Breezy!

Reviewed commit: 4414e2ff38

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[github-actions]

🎉 This PR is included in version 2.27.1 🎉

The release is available on GitHub release

Your semantic-release bot 📦🚀