docs: project planning and architecture design
- Add ADR.md documenting all technology stack decisions with rationale
- Create comprehensive ROADMAP.md with 10-phase implementation plan
- Add 3 architecture diagrams (AWS infrastructure, application stack, network)
- Document collaboration guidelines in `.github/copilot-instructions.md`
- Technology stack descisions: AWS, Terraform, Ansible, Docker Compose, PostgreSQL
Phase 1 establishes foundation for automated Gitea deployment with
proper decision tracking and incremental development approach.
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