0.9.0

Add Rust translation and reorganize codebase

• Reorganize JavaScript source files into js/ folder structure
• Move tests from root tests/ to js/tests/
• Add complete Rust translation in rust/ folder with:
• Shell parser supporting &&, ||, ;, |, (), and redirections
• All 21 virtual commands (cat, cp, mv, rm, touch, mkdir, ls, cd, pwd, echo, yes, seq, sleep, env, which, test, exit, basename, dirname, true, false)
• ProcessRunner for async command execution with tokio
• Comprehensive test suite mirroring JavaScript tests
• Case study documentation in docs/case-studies/issue-146/

Related Pull Request: #147

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