(Personal Targeted Spells) Fix mover misaligned with icons in edit mode

[Krathe82]

Summary

• The edit mode mover box was misaligned with where Personal Targeted Spell icons actually appear. The mover's centre sat at icon 1's position, so the mover extended in the growth direction past the icons rather than surrounding them symmetrically.
• The saved position (personalTargetedSpellX / Y) now represents the visual centre of the icon block. A new GetPersonalContainerPoint helper offsets the container by (maxIcons-1)/2 * (size+spacing) opposite to the growth direction, keeping icons centred on the saved point.
• A one-time migration in Core.lua (MigratePersonalContainerPosition) shifts existing saved positions by the same halfBlock in the growth direction on first load, so icon 1 stays at its old screen location for existing users.
• CENTER_H and CENTER_V growth directions are already symmetric and require no adjustment.

Test plan

• Open Personal Targeted Spells edit mode — mover box should be centred on the icon block, not offset to one side
• Drag the mover to a new position — icons follow correctly and mover stays aligned
• Test each growth direction (LEFT, RIGHT, UP, DOWN, CENTER_H, CENTER_V) — mover aligns correctly in all cases
• Reload after first fix application — existing saved position preserved visually (icon 1 stays where it was)

[DanderBot]

Thanks for the PR! Merged into main and will ship in the next alpha build.