MidnightNameplates 0.10.2.4 - Confirmation Modal Fix

ROOT CAUSE
The Phase 10.2.3 import/export confirmation was parented to the Profiles
scrolling content page. It therefore rendered inline over the normal profile
controls instead of behaving like a modal dialog.

FIX
- Import/export confirmation is now parented to the main config frame.
- Centered over the config window.
- DIALOG strata / elevated frame level.
- Added a dark mouse-blocking overlay behind the dialog.
- Confirm and Cancel both close the overlay.
- Confirmation no longer changes or overlaps Profiles page layout.

TEST
1. Profiles -> Generate Export.
2. Dialog should appear centered over the config window.
3. Background config should be dimmed and non-clickable.
4. Cancel should close it without generating.
5. Generate again -> GENERATE should close modal and create string.
6. Preview an import -> IMPORT -> confirmation should use same centered modal.
7. No controls should overlap the dialog.
8. Profile delete confirmation remains separate and functional.
9. No Lua errors.
