Add Copywriter agent to Launch phase

[xiapeli]

Summary

The Launch phase needs a Copywriter agent to generate marketing copy, release notes, app store descriptions, social media posts, and landing page content. This agent would take the product context from upstream phases and produce publication-ready text.

Suggested Approach

1. Create a new agent definition file in the Launch phase directory
2. The agent should receive product description, features list, and target audience from upstream agents
3. Consider using Sonnet 4.6 for high-quality creative writing with good cost balance
4. Output should include multiple copy variants (short/medium/long) for different channels

Acceptance Criteria

• Agent definition file created with clear I/O contracts
• Model selection justified (creative writing quality vs cost)
• Quality gates defined (e.g., tone consistency, no AI cliches, character limits respected)
• Output format supports multiple channels (App Store, social media, email, landing page)
• Integration with Launcher agent documented
• Example input/output provided

Notes

• The agent should avoid common AI writing patterns ("revolutionary", "seamlessly", "cutting-edge")
• Copy should be adaptable to different tones (professional, casual, technical)
• Consider multilingual support as a future enhancement