JPDFium's published artifacts target JVM 25 and Stirling-PDF's main
sources are now compiled with sourceCompatibility = VERSION_25, so JDK
21 is no longer supported. Update header comments and developer-facing
docs to reflect the hard floor.
- backend-build.yml header: 'JDK 21/25 \xc3\x97 spring-security' -> 'JDK 25 \xc3\x97 spring-security'
- AGENTS.md Important Notes: minimum 21 -> requires 25
- DeveloperGuide.md prerequisites + setup steps: drop 'or later, 25 recommended'
language, say 'JDK 25' outright.
Anthony Stirling
3626319685