Fix (link ticket to problem) missing entity check when linking tickets to a problem via massive action

[Herafia]

Checklist before requesting a review

Please delete options that are not relevant.

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.
• This change requires a documentation update.

Description

• It fixes !45187
• When linking tickets to a problem via the "Link to a problem" massive action, no entity restriction was applied, allowing tickets from unrelated entities to be linked. The problem dropdown is now filtered by the active session entity, and each ticket is validated against the problem's entity before the link is created. This aligns the massive action behavior with the existing manual linking logic in Problem_Ticket.

Screenshots (if appropriate):

[Rom1-B]

No test covers link_to_problem (src/Ticket.php:2917-2990), and none is added. Missing cases:

• same-entity (accepted)
• cross-entity non-recursive (rejected)
• recursive parent problem on child-entity ticket (accepted)

[stonebuzz]

with tests