Character sheet: fix issues with scroll and section visibility

[Snsei987]

What does this PR do?

Fixes 3 bugs, maybe more:

• When scrolling all the way down, then collapsing sections, depending on how many sections were collapsed scroll would be impossible (intended behavior with scroll frame height).
• After a /reload, opening the character sheet and clicking up/down section button or clicking on a section title (to collapse/show it) would make the hidden sections reappears.

How was it tested?

12.0.7 only. After a /reload and in M+.

Screenshots

First issue with scroll:

Before:

After:

Second and third issues:

My config:

Before:

After:

Checklist

• N/A New settings default OFF (no behavior change without opt-in)
• N/A Zero cost while disabled: no events registered, no polling, no hooks doing work, no frames built
• Cheap while enabled: event-driven (no polling, no timer-based logic, no per-frame allocations)
• N/A No writes onto Blizzard-owned frames (weak-table pattern used); HookScript/hooksecurefunc only, never SetScript on Blizzard frames
• Tested in-game, works on live retail; no load errors on the 12.1 PTR client