refactor(guestbook): migrate to use case architecture
- fix TypeError: nullable manage URLs in GuestbookEntryMetaDTO
- enforce manage access server-side: edit/delete/reply check author rights (403)
- unify mode/access checks in GuestbookMode and GuestbookAccess, drop GuestbookService
- add use cases: create, edit, reply, delete, clear + context/ensure-access guards
- move all data access to GuestbookEntryRepositoryInterface, add ClearGuestbookPeriod enum
- extract text formatting from model to GuestbookEntryTextFormatter (profile activity updated)
- use PageMeta for paginated titles, Session service instead of $_SESSION
- escape user text at output in templates instead of controllers
- log previously swallowed exceptions in captcha and attached files cleanup