- Fixed MNIST MLP to use manual cross-entropy (losses module not exported)
- Removed incorrect CrossEntropyLoss and Adam imports from MNIST example
- Updated training to use simple SGD instead of Adam for Module 8 compatibility
- All 5 milestone examples now tested and working:
* Perceptron 1957 ✓
* XOR 1969 ✓
* MNIST MLP 1986 ✓
* CIFAR CNN Modern ✓
* GPT 2018 ✓