Add requirements.txt for reproducible environment setup

[abhiram123467]

What This PR Does

Adds requirements.txt listing all dependencies needed
to run the ArtExtract notebooks.

Why

Currently there is no requirements.txt — contributors
have to manually figure out dependencies. This makes
setup as simple as:
pip install -r requirements.txt

Testing

Verified all packages install correctly on Python 3.10.

Related to my GSoC 2026 application for ArtExtract.

[agentksimha]

does this add requirements.txt for both Artextract repos ?

[abhiram123467]

does this add requirements.txt for both Artextract repos ?

Yes, this requirements.txt covers dependencies for both
ArtExtract tasks:

1. Task 1 (Style/Artist/Genre Classification) — ResNet50,
   BiLSTM, Isolation Forest
2. Task 2 (Painting-in-a-Painting Detection) — EfficientNet,
   Siamese network, Triplet Loss, KNN retrieval

All packages listed support both pipelines. Happy to split
into separate files if preferred!

[agentksimha]

Ohhhk makes sense