- Remove platform-specific code (ARM_MATH_CM33, XMOS __XS3A__, std::printf)
- Add set_output()/set_outputs()/add_example() API for programmatic training
- Fix release build crash: side effect inside assert() for loss function init
- Replace fake smoke test with real convergence tests (5 tests, all pass)
- Rewrite example to demonstrate actual training with real output
- Update README, CHANGELOG, and extraction plan to match reality
