docs: add comprehensive AI assistant integration guide

- Create AGENT.md with detailed guide for OpenCode, Gemini CLI, and Claude usage
- Document AI-assisted packaging workflow and best practices
- Include prompt templates and context sharing strategies
- Add symbolic links GEMINI.md and CLAUDE.md for easy access
- Update README.md to reference AI assistant documentation

AI Integration Features:
- Phase-specific assistant recommendations (Research→Gemini, Development→Claude, etc.)
- Template-driven development with AI assistance
- Quality assurance workflows with AI review
- Multi-assistant collaborative approaches

This establishes AI-first development approach for the 56-application packaging initiative,
significantly accelerating development while maintaining quality standards.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -168,6 +168,12 @@ Each Cloudron package requires:
 - **Mounted**: Repository at `/workspace`
 - **Persistent**: Survives across development sessions
 
+### AI Coding Assistants
+- **[AGENT.md](AGENT.md)**: Comprehensive guide for using OpenCode, Gemini CLI, and Claude
+- **[GEMINI.md](GEMINI.md)**: → Symbolic link to AGENT.md
+- **[CLAUDE.md](CLAUDE.md)**: → Symbolic link to AGENT.md
+- **Usage**: Accelerate development with AI-assisted packaging
+
 ### Helper Scripts
 - **`UpstreamVendor-Clone.sh`**: Clone all upstream repositories
 - **`UpstreamVendor-Update.sh`**: Update existing checkouts