docs: add comprehensive contributing guidelines for community contributors

[ipagent961051]

Description

This PR adds a comprehensive CONTRIBUTING.md file to establish clear guidelines for new contributors. The repository currently lacks documentation on how developers can contribute, which is essential for community growth.

Changes Made:

• ✅ Complete contribution workflow guide
• ✅ Code style and testing requirements
• ✅ GEP-A2A protocol compliance checklist
• ✅ Priority-based contribution types (High/Medium/Nice-to-Have)
• ✅ First PR submission instructions
• ✅ License agreement and contact information

Why This Matters:

Many potential contributors don't know how to start contributing. This documentation will:

• Reduce friction for first-time contributors
• Ensure GEP-A2A protocol compliance in all contributions
• Establish consistent code quality standards
• Accelerate community growth and collaboration

Review Notes:

• Follows conventional commits format for commit messages
• Aligned with PEP 8 and best practices
• Includes both technical requirements and community guidelines
• Ready to be used by all future contributors

Type: docs
Impact: High (enables future contributions)
Testing: None required (documentation only)