Adds a "Display Mode" dropdown to the targeted spells indicator settings:
- Icons: spell cast icons shown, glow only on listed spells (original)
- Border: frame border glow only, no icons
- Both: icons + border glow on any targeted cast

In Border/Both modes, all enemy casts targeting group members trigger
the glow, not just listed spells. Icon display respects the existing
num/size/orientation settings.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>