docs: [#21] add comprehensive application installation automation plan

- Create detailed implementation plan for Phase 3: Maximum Practical Application Installation Automation
- Document current state analysis with accurate status of implemented vs missing components
- Provide technical implementation details for SSL certificate automation and MySQL backup automation
- Include testing strategy with unit, integration, SSL workflow, and end-to-end testing approaches
- Define success criteria focusing on 90%+ automation with minimal manual steps
- Add risk assessment and mitigation strategies for high-risk areas
- Establish timeline and dependencies for SSL automation (Week 1) and MySQL backup automation (Week 1-2)
- Document extension points for existing twelve-factor deployment workflow
- Include comprehensive crontab template integration and cloud-init automation
- Provide detailed technical specifications for supporting scripts and environment template updates

Critical Review Findings:
- Updated status table to reflect actual repository state (40% complete, 4/12 components)
- Identified missing files: mysql-backup.sh, crontab_utils.sh
- Clarified nginx template state (HTTP active, HTTPS commented out)
- Corrected environment template status (SSL/backup variables already present)
- Fixed all markdown linting issues and improved documentation structure

This plan provides the foundation for implementing maximum practical automation while maintaining
the existing robust twelve-factor deployment architecture.

Author: josecelano