Add Adanos Finance Sentiment API research notebook

[alexander-schneider]

Summary

• add an example notebook for researching external stock sentiment with Adanos
• add the notebook to the resources page

Why this is useful

The notebook shows how vectorbt users can treat Adanos Finance Sentiment API as an external research input rather than a core dependency. It fetches source-level sentiment, builds simple composites such as average buzz and bullish average, combines them with a lightweight vectorbt price filter, and ranks candidates for further research.

Scope

This PR is intentionally limited to docs and examples.

It does not add:

• new core dependencies
• vendor-specific loaders in the vectorbt core
• API key handling in the library itself