feat(player-aura-bars): Add Border Style settings to Player Aura Bars in the Unit Frames module

[Ricoder92]

Summary

Adds a Border Style setting to Player Aura Bars in the Unit Frames module. Border textures can now be configured independently for the default and custom Buff/Debuff bars.

Changes

• Added built-in and LibSharedMedia border texture selection
• Added border offset, shift, and layer controls
• Added support to the live bars, preview, sync actions, and weapon enchant icons
• Prevented incompatible combinations of textured borders and custom icon shapes
• Preserved the existing Solid border as the default appearance

Taint / Secret-Value Safety

Textured borders use addon-owned texture regions attached to the existing addon-owned border host. No aura data is read, no protected attributes are modified, and no custom state is written onto Blizzard-owned aura buttons. The implementation avoids BackdropTemplate calculations on restricted aura geometry.

Checklist

• New settings default OFF — N/A: Border Style defaults to Solid, preserving the existing appearance
• Zero cost while disabled — no new events, hooks, or update loops
• Cheap while enabled — textured border regions are created lazily and require no per-frame updates
• No writes onto Blizzard-owned frames — state remains in external tables and addon-owned child regions
• Tested in-game on live