PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*.
  IMPORTANT: Do NOT purge/delete any folders/files (e.g. tests) when regenerating the samples as manually written tests may be removed.
• File the PR against the correct branch: master (upcoming 7.x.0 minor release - breaking changes with fallbacks), 8.0.x (breaking changes without fallbacks)
• If your PR solves a reported issue, reference it using GitHub's linking syntax (e.g., having "fixes #123" present in the PR description)
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

Summary by cubic

Adds first-class validation for Spring Pageable params and sort fields in generated spring and kotlin-spring servers. Automatically applies @ValidPageable/@ValidSort, and preserves OpenAPI defaults via @PageableDefault.

• New Features
  • generatePageableConstraintValidation: generates @ValidPageable + validator; auto-applies when page/size have max constraints; enforces maxSize/maxPage.
  • generateSortValidation: generates @ValidSort + validator; allowed sort values derived from a sort enum (inline or schema).
  • Auto-detects pageable via page/size/sort or x-spring-paginated; autoXSpringPaginated can add the extension; sets @PageableDefault(page, size) from schema defaults.
  • Implemented for spring and kotlin-spring (spring-boot) with new templates (validPageable.mustache, validSort.mustache) and SpringPageableScanUtils; docs updated (including autoXSpringPaginated); new samples samples/server/petstore/springboot-sort-validation and samples/server/petstore/kotlin-springboot-sort-validation (added to CI).

^{Written for commit 737aa46. Summary will update on new commits.}