Initial open source release with CC BY-NC-SA 4.0 license

- Add complete CC BY-NC-SA 4.0 International License
- Add comprehensive README with project description and usage
- Add CONTRIBUTING guidelines for developers
- Add Nix development environment with OpenSCAD tooling
- Add .gitignore for OpenSCAD and Nix projects
- Add copyright headers to source files

.gitignore

@@ -0,0 +1,40 @@
+# Cuatro Project - .gitignore
+
+# OpenSCAD generated files
+*.stl
+*.3mf
+*.amf
+
+# Build artifacts
+build/
+output/
+
+# Temporary files
+*.tmp
+*~
+.DS_Store
+Thumbs.db
+
+# Editor files
+.vscode/
+.idea/
+*.swp
+*.swo
+
+# OS files
+.DS_Store
+desktop.ini
+
+# Print logs and slicing files
+*.gcode
+*.bgcode
+*.3mf
+*.factory
+
+# Nix
+result
+result-*
+.direnv/
+
+# Development environment
+.envrc