JSON preview no longer exposes internal GraphQL error details

The JSON preview client now replaces GraphQL error messages with a generic notice before rendering. The original message is still available in the preview client's log at DEBUG level for troubleshooting.

(CMS-31184)

Fix NullPointerException when parsing X-Preview-Date HTTP header

Fixed a bug in the Headless Server's media delivery endpoint where a NullPointerException caused erroneous error responses for preview requests. The X-Preview-Date header value was incorrectly passed to Long.getLong(), which looks up a JVM system property by name rather than parsing a numeric string. The header is now correctly parsed as an RFC 1123 HTTP date using DateTimeFormatter.RFC_1123_DATE_TIME. Malformed date values are gracefully handled with a warning log, and the current date is used as a fallback.

(CMS-31035)

Remote Link DataLoader Lookup

Remote link resolution now looks up the DataLoader from the per-request execution context instead of holding a singleton field reference.

(CMS-30790)