Fix: multiple HTML rendering and crash bugs in PDF exports

[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 !43955

• TypeError crash when exporting Problems or Changes with linked items that lack serial/otherserial columns (e.g. Software, User): fixed by using null-coalescing fallback before Toolbox::stripTags().

• Description rendered as a single block in Problem and Change PDFs: Toolbox::stripTags() was stripping HTML structure before displayText(), which expects HTML. The strip call is removed.

• Change analysis and plan fields showing raw HTML: fields were embedded in the label argument via sprintf() instead of being passed as the content argument to displayText(). Fixed argument placement; also removed ineffective setColumnsSize(10, 90) calls before displayText() (which forces 100% internally).

• Ticket approval comments showing HTML fragments: comment fields were stored with HTML entities not decoded before PDF rendering. Fixed using html_entity_decode().

TODO: same PR on main