CELDEV-1334 Add navigation REST API

[fpichler]

https://synjira.atlassian.net/browse/CELDEV-1334

Summary

• add celements-navigation-rest with the public /api/v1/navigation/{nodeSpace} contract
• enforce current-wiki canonical references, caller-relative rights filtering, localized titles and URLs, stable segmented JSON, and safe errors
• expose OpenAPI documentation and apply Cache-Control: private, no-store to successful and error responses
• cover request validation, guest/authenticated rights behavior, expansion, ordering, mandatory-value omission, JSON, errors, and OpenAPI

Coordinated delivery

Draft 2 of 4 for CELDEV-1334:

1. CELDEV-1334 Add current-wiki REST reference ADR celements-spring#31
2. CELDEV-1334 Add navigation REST API #309
3. CELDEV-1334 Manage navigation REST artifact celements-parent-poms#142
4. CELDEV-1334 Deploy navigation REST component celements-web#556

Validation

• offline clean verify: 43 tests, zero failures/errors
• Maven dependency analysis: no problems
• formatter, diff check, and fully-qualified-name scan: clean
• packaged REST JAR matched the copy embedded in the coordinated webapp WAR
• local guest and error-contract runtime smoke checks passed
• manually tested and approved by the requester

[msladek]

thanks for the changes, lgtm