Add Perplexity integration attribution

[qirh]

Description

Perplexity would like to identify requests from the Sema4.ai Perplexity action package.

This adds X-Pplx-Integration: sema4ai to the existing request headers. The API endpoint, authorization, payload, and response parsing are unchanged.

How was this tested?

The action's actual request boundary was exercised with a stubbed HTTP transport. It sent the existing authorization and content-type headers plus the new integration header to the unchanged Perplexity endpoint.

Checklist

• Bumped the Action Package patch version.
• Performed a self-review.
• Updated the package changelog.
• Documentation remains accurate because there is no user-visible behavior change.
• No OAuth scope changes are involved.

[qirh]

@raivolink @mikahanninen when you get a chance, could one of you approve the actions test run here and review? It is a single header added to the Perplexity action package, with the patch version bump and changelog entry.