DOC: clarify that clustering example images are clickable

[Priyanshu7439]

Summary

Adds a note in the clustering documentation to make it clearer that example images are clickable and link to the full examples.

Motivation

Currently, it is not obvious to users that images in the clustering guide are interactive. This change improves discoverability and overall user experience.

Reference Issues/PRs

Related to scikit-learn#30596

What does this implement/fix? Explain your changes.

• Added a .. note:: directive below the figure in clustering.rst
• This explicitly informs users that the image is clickable and leads to the full example

AI usage disclosure

I used AI assistance for:

• Code generation
• Test/benchmark generation
• Documentation (including examples)
• Research and understanding

Any other comments?

This is a small documentation improvement aimed at improving usability.