Rename the entire project from "Validatrix" to "Nimcheck" in README.md, Makefile, LESSONS_LEARNED.md, and all source references; add initial Gitea CI workflow with lint, test, and build jobs for Nim 2.0.0; expand .gitignore with comprehensive patterns for Nim, Python, editor, environment, and temporary files; add CONTRIBUTING.md and LICENSE (MIT) files to establish project governance and licensing.
