Add Free JEV API Guide to reference resources

[erickkkyt]

Suggestion

Add Free JEV API Guide to Reference and Documentation. It provides a runnable first-request walkthrough and practical examples for developers integrating Jev's typed decision API.

Scope and affiliation

I am affiliated with the BeatAPI team, which publishes this independent guide. The site states that API access and accounts are handled on BeatAPI. This submission links directly to the guide's HTTPS homepage without referral or tracking parameters.

I searched the list, open/closed issues, and pull requests for an existing JEV API entry. git diff --check passed.

[CLAassistant]

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