Add Releases changelog page (May 2026, tag 2605)

[Nesmeshnoy]

Summary

• Replaces the WIP placeholder in docs/releases.md with the first real Releases page: a combined changelog for the May 2026 release (image tag 2605) covering the Interop APIs, Prior Auth (ePA) APIs, and the FHIR App Portal.
• Each component heading links to its Docker Hub image; the intro states the Aidbox dependency in one line. No setup steps here — those live in Get Started / Run Payerbox.
• Compiled from merged PR history and verified against source; uses doc-relative links only (no source-repo links). All 22 internal links validated against the current page tree.

Depends on

• Fix DTR docs: prefill is FHIRPath, not CQL #8 (DTR docs: CQL → FHIRPath). The DTR entry here states FHIRPath prefill; merge Fix DTR docs: prefill is FHIRPath, not CQL #8 first or together so the linked DTR pages agree.

Test plan

• Page renders on the docs site; headings and in-heading image links work.
• All "See …" links resolve.
• Merge after/with Fix DTR docs: prefill is FHIRPath, not CQL #8 so the DTR pages are consistent.

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