docs: Add comprehensive OpenSSF Best Practices Badge application guide

Created step-by-step guide for OpenSSF badge application process:

OPENSSF_APPLICATION_GUIDE.md - Complete Application Instructions:
- Pre-application checklist (all prerequisites met ✅)
- Step-by-step application process (6 phases)
- Detailed answers to all 60+ badge criteria questions
- Honest disclosure of 32% coverage with documented trajectory
- Expected initial score: 50-60% passing
- Timeline: Passing Badge by Q2 2025

Key Sections:
1. Account creation and project setup
2. Badge criteria answers (Basics, Change Control, Quality, Security, etc.)
3. Test coverage response: Honest 32% with clear 70%/90% plan
4. Security: 0 vulnerabilities, comprehensive tooling
5. Documentation: Complete (README, CONTRIBUTING, CODE_OF_CONDUCT, GOVERNANCE)
6. Post-submission: Badge integration, public tracking, regular updates

Application Strategy:
- Apply NOW with honest current state (32% coverage)
- Demonstrate commitment via public accountability
- Show clear trajectory: 70% (Q1 2025), 90% (Q2 2025)
- Regular updates every 2 weeks

Ready to Apply: All prerequisites complete
- ✅ CodeQL workflow
- ✅ GOVERNANCE.md
- ✅ SECURITY.md
- ✅ 887 passing tests
- ✅ 0 security vulnerabilities
- ✅ Comprehensive documentation

Next Step: User submits application at https://bestpractices.coreinfrastructure.org/

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

Co-Authored-By: Claude <[email protected]>

Author: GeneAI