MIDNIGHTNAMEPLATES — PHASE 11.7.1
DYNAMIC PAGE HEIGHT + PREVIEW CENTERING

FIX 1 — PER-PAGE SCROLL RANGE
Each config page now measures its visible controls/regions and sizes its own
scroll canvas to the real content height.

Expected:
- Short pages stop at their final option.
- Long pages retain their full scroll range.
- No large empty tail below short pages.
- Conditional controls can change the page height.
- Switching pages recalculates the scroll range.
- If a page becomes shorter while scrolled down, its scroll position is clamped.

FIX 2 — LIVE PREVIEW CENTERING
The preview composition is moved toward the true visual center of the stage.
Aura/cast compensation remains active so different plate families do not simply
anchor the raw health bar to the middle.

TEST
1. Open every category and scroll to the bottom.
2. Verify scrolling stops shortly after the last visible control.
3. Compare a short page (Threat/General) with a long page (Summons/Rules).
4. Toggle controls that reveal/hide dependent settings, then re-check the bottom.
5. Switch pages while one page is scrolled to the bottom.
6. Check Live Preview: Enemy NPC, Enemy Player, Friendly Player, Friendly Pet,
   Enemy Pet, Guardian and Totem.
7. Check preview with auras and cast bar visible.
8. No Lua errors, taint, protected-action, secret-value errors or FPS regression.

No runtime nameplate or summon-source architecture was changed.
