Add project README and todo checklist with workflow updates

[brasga-a]

This pull request makes significant progress in rebranding the project from "Luna" to "Shell" and updates documentation, configuration, and crate naming to reflect this change. It also introduces a new README.md and a comprehensive TODO.md checklist to guide development and clarify architecture, module structure, and contributor expectations.

Project rebranding and documentation updates:

• Renamed all references from "Luna" to "Shell" across documentation files such as AGENTS.md, context/README.md, and context/milestones.md, ensuring consistent project identity. [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

Crate and configuration alignment:

• Updated crate names in Cargo.toml and throughout documentation from luna-module-* to shell-module-* to match the new project naming convention. [1] [2] [3] [4] [5] [6] [7] [8] [9]

Major documentation additions:

• Added a new README.md detailing the purpose, architecture, design goals, stack, workspace structure, module philosophy, configuration, development status, build instructions, quality gates, contribution guidelines, and license for the Shell project.

Development process improvements:

• Added a new TODO.md file with a detailed, categorized checklist (in Portuguese) to track current tasks, module implementation steps, infrastructure plans, and quality assurance measures for the project.

These changes lay the groundwork for a clear, unified project direction and improve the onboarding experience for contributors.