Document ICPR2026 public notebooks

[wonderalexandre]

Summary

• add the public ICPR2026 notebooks for plant and screw segmentation
• document each notebook with English Markdown and code docstrings
• keep saved outputs in English and rename notebooks to ConvNet, ID3-NN, and Unet naming

Validation

• parsed all six notebooks as JSON
• parsed all code cells with Python ast
• checked that all functions/classes have docstrings
• checked for Portuguese-like strings in code and textual outputs

Scope

Only notebooks/ICPR2026 is included. downloads/ and notebooks/ICPR2026_run remain uncommitted.