Update ML/NLP README docs with completed notebook inventory and refreshed status dates

[Copilot]

This updates repository documentation to reflect completed coursework artifacts now present in source control. It adds explicit notebook coverage and dataset/dependency notes across root, ML, and NLP README files, and refreshes status metadata to 2026-09-09 where required.

• Root README (README.md)

  • Added “Completed notebooks & new highlights (summary of what's now included)” between quick highlights and status/setup content.
  • Documented representative newly included notebooks across ML/NLP and summarized data sources (sklearn built-ins, Colab/Drive-mounted data, custom image folders, pretrained vectors/packages).
  • Kept the status block current with Last updated: 2026-09-09.

• ML README (ml/README.md)

  • Appended “Completed notebooks & data notes (ML)” with representative notebook paths and concise run/data expectations (sklearn datasets, mounted/custom data, GPU recommendation for CNN/Autoencoder notebooks).

• NLP README (nlp/README.md)

  • Updated status line date to 2026-09-09.
  • Appended “Completed notebooks & highlights (NLP)” plus dependency/data notes for pretrained vectors and transformer workflows.

Example of the added documentation pattern:

## Completed notebooks & new highlights (summary of what's now included)
...
Datasets & data sources used in notebooks (examples)
- sklearn built-in datasets (wine, make_blobs, etc.)
- Google Drive / Colab-mounted data ...
- Custom image folders ...
- Pretrained vectors and third-party packages ...