MidnightNameplates Phase 9.3.7 - Live Preview Layout Rebuild

This replaces the failed "just make it bigger" approach.

Changes:
- Preview is wider rather than excessively tall.
- Preview-only health bar width is 220-320px depending on configured live width.
- Preview-only health height is 18-30px.
- Real in-game Width / Height / Scale values are NOT changed.
- Removed 1.55x blanket preview magnification.
- Aura vertical spacing tightened.
- Cast-bar compensation reduced.
- Name text remains readable without becoming oversized.
- Preview stage now uses 500x158 inside a 520x190 preview frame.
- Main config remains 1020x760.
- Page content starts slightly higher so the preview does not waste vertical space.

Test:
1. /mnp opens.
2. Preview should look wider and cleaner, not just enlarged.
3. Auras should sit closer to the nameplate.
4. Cast bar should remain centered beneath the health bar.
5. General page should begin closer to the preview.
6. Real in-game nameplate dimensions must remain unchanged.
7. No Lua errors.
