feat(refactor-module-logic): Create implementation plan and design artifacts

feat(refactor-module-logic): Create implementation plan and design artifacts This commit introduces the technical implementation plan for the module refactoring feature (003-refactor-module-logic). It includes the following design artifacts: - research.md: Justification for the chosen modular structure. - data-model.md: Documentation of the data objects passed between modules. - contracts/cli-contract.md: A contract ensuring the CLI remains stable. - quickstart.md: Instructions for verifying the refactoring. - plan.md: The central implementation plan. This completes the design phase and prepares the feature for task breakdown and implementation.