Expose initial / historical news sentiment insights for backtesting stability

Problem

News sentiment insights are updated retroactively over time. While this is expected behavior, the API currently only exposes the latest sentiment (insights.sentiment) and does not allow access to the initial or historical sentiment states.

This makes historical backtesting unreliable, since sentiment values used in past simulations no longer match what was available at the time of execution.

Concrete example

For request id
9eba2c7bac1eb14b9fae9ddf1a64f7dead45de8d5e5dc3bcbea9d56b9744003d
the sentiment was initially positive and later changed to neutral, breaking reproducibility.

Proposed solution (one possible design)

Expose sentiment history instead of only the latest state. For example:

• Allow insights to include multiple entries over time (with timestamps / versioning), or
• Add an optional way to fetch the initial insight only, or

Use case

Deterministic backtesting and reproducible research for quantitative trading systems.

The issue names no files or tests; first locate the TypeScript API-client code that exposes insights.sentiment and inspect the response for request id 9eba2c7bac1eb14b9fae9ddf1a64f7dead45de8d5e5dc3bcbea9d56b9744003d. Clarify whether the client should expose initial values, timestamped history, or another versioned representation, then verify that backtesting can reproduce the sentiment available at execution time.