Add per-indicator pandemic borders to raid-frame buffs

[andybergon]

What does this PR do?

Adds an opt-in pandemic border to raid-frame buff icon indicators. Lifebloom is one example of a buff whose pandemic window is useful to track: timing the refresh preserves its bloom heal instead of refreshing too early. The border can be configured per buff icon indicator, with customizable color and thickness. Duration and stack text remain readable, and threshold text stays independent.

The selected indicator previews the active border in settings. I recognize the current pause on feature submissions; this is a small feature for consideration when that window reopens.

How was it tested?

• Tested in-game with Lifebloom on live; screenshots show the border absent at 12 seconds and active at 3 seconds, with stack text visible. The tester confirmed it works. Exact client build was not recorded.
• Both changed files pass Lua 5.1 syntax checks.
• Focused mocked checks cover enable/disable, color, thickness, text layering, Hide Icons, unsupported API handling, and one-time registration. These checks do not simulate Blizzard's protected aura engine.

Screenshots

Outside the refresh window:

Inside the refresh window:

Settings:

Checklist

• New settings default OFF.
• Zero cost while disabled: exception requested. One holder and four textures are created and registered per icon at creation, even when disabled, so enabling later does not require registration against a protected aura button. Disabled borders use transparent textures. No polling, events, or hooks are added.
• Cheap while enabled: Blizzard drives pandemic visibility; no polling or timer-based logic.
• No custom fields or scripts added to Blizzard-owned frames; state stays in AuraKit's data table and the border uses the supported region registration API.
• Tested in-game on live; no pre-Midnight APIs or numeric version gates. Registration checks whether AddPandemicRegion is available.