Following the clean pattern from Modules 01 and 05:
- Removed demonstrate_complete_networks() from Module 03
- Module now focuses ONLY on layer unit tests
- Created tests/integration/test_layers_integration.py for:
* Complete neural network demonstrations
* MLP, CNN-style, and deep network tests
* Cross-module integration validation
Module 03 now clean and focused on teaching layers
Module 04 already clean - no changes needed
Both modules follow consistent unit test pattern