Fix: correct entity and ticket validation in credit forms

[Rom1-B]

Checklist before requesting a review

Please delete options that are not relevant.

• I have performed a self-review of my code.
• I have added tests (when available) that prove my fix is effective or that my feature works.
• I have updated the CHANGELOG with a short functional description of the fix or new feature.
• This change requires a documentation update.

Description

• It fixes #N/A
• This fixes several forms and endpoints of the Credit plugin so that voucher creation, voucher configuration and ticket consumption records are always validated against the correct entity and the correct ticket.
• Previously some of these checks were missing, inverted, or applied to the wrong record, which could let a request affect a voucher or a ticket outside the caller's expected scope.
• The consumption history view and the quantity preview endpoint now also verify entity access before returning data.

Screenshots (if appropriate):