- Add tofu.build module with runMakepkg() public API
- BuildException for missing binary, non-zero exit, missing output
- Real-time stdout/stderr streaming with last-20-lines stderr capture
- Conditional --force flag based on force parameter
- zetaToolchainPath resolution from Config
- 7 unittests using fake zeta-makepkg shell scripts
- pipeProcess + Redirect.stderr for tee approach
