docs: add changelog entry for 2026.4.0–2026.5.0

[mintlify]

Summary

Adds a combined changelog entry covering releases 2026.4.0, 2026.4.1, and 2026.5.0, plus the GHSA-c3fq-x5hm-p482 published-docs security fix.

Changes

• New features: OpenAPI 3.1 export, collection-level scripts, desktop zoom and update check, keyboard layout strategy, configurable proxy URL, SMTP OAuth2, configurable webapp-server timeouts, Mongolian translation.
• Updates: API docs publishing UX, translations, accessibility, variable tooltip, OAuth2 id_token support.
• Bug fixes: GHSA-c3fq-x5hm-p482 published-docs access check, secret variable leak, mass-assignment hardening, script imports on WebKit, magic-link sign-in for org cloud, proxy load order, $randomUUID RFC 4122 compliance, Postman import resilience, mock server domain URL, team subfolder write-access, GQL history schema, personal workspace docs publishing, dependency CVE patches.

Context

Triggered by hoppscotch/hoppscotch#6386 (GHSA-c3fq-x5hm-p482). The last changelog entry covered 2026.3.0/2026.3.1; this entry catches up the published changelog with everything shipped since then.