Set up and build iTerm2 from source for local development. Use when: (1) Setting up the iTerm2 development environment from a fresh clone, (2) Troubleshooting build failures (code signing, Xcode version mismatch, missing Metal Toolchain), (3) Running iTerm2 tests, (4) Rebuilding after Xcode updates. Triggers: "build iterm2", "setup iterm2", "dev environment", "build fails", "make Development", "code signing error", "xcode version mismatch".