Introduced a comprehensive roadmap in `ROADMAP.md` to outline
the vision, purpose, and development phases of the
`DocumentOperator` service. Key additions include:
- Table of contents for navigation.
- Project overview with problem statement, solution, and core
features.
- Business workflow description for API operations.
- Architecture and design decisions:
- Clean Architecture principles and dependency rules.
- CQRS with MediatR and Vertical Slice Architecture.
- Exception-based error handling and Minimal APIs.
- Multi-tenancy strategy using API keys.
- Technology stack and detailed project structure.
- Development roadmap with nine phases, highlighting current
progress (Phase 1 completed, Phase 2 in progress).
- Learning notes, references, and an update log.
The roadmap serves as a living document to guide development
and ensure alignment on goals and strategies.
