feat: quiet mode for CLI runs

[vaporwavie]

Issue for this PR

Closes #6999

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

This PR adds the -q | --quiet argument, which aims to provide a cleaner output to the user for CLI runs, suppressing tool calls and focusing on the actual response from the agent. Since this is a stainless run, it won't allow asking for permissions or anything that defeats the purpose of a quiet mode.

How did you verify your code works?

• Ran bun turbo typecheck successfully via the pre-push hook, had to fix a couple of type issues
• Smoke-tested opencode run -q locally using:
  • bun run --conditions=browser src/index.ts run -q -m opencode/gemini-3-flash "list me the files in this directory"
  • bun run --conditions=browser src/index.ts run -q -m opencode/gemini-3-flash "list me the files in this directory" | cat
• Confirmed quiet mode suppresses tool-call output, keeps the spinner in TTY mode, and prints only the final response

Screenshots / recordings

opencode-quiet-mode.mov

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

If you do not follow this template your PR will be automatically rejected.

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