Add --dry-run flag to preview generated test prompt

### Problem
When debugging micro-agent behavior, there's no way to preview what test prompt will be sent to the LLM without actually running it.

### Proposed Solution
Add a (or ) flag that outputs the generated test prompt to stdout and exits without making any LLM calls or file changes.

Example:
```sh
micro-agent ./utils.ts -t "npm test" --dry-run
# Outputs generated test prompt to stdout, no execution
```

### Use Case
Useful for debugging, verifying prompt engineering, and teaching how micro-agent works before committing to execution.