Add new localization strings for UI customization

[Crazyyoungs]

What does this PR do?

Updated and completed the Korean (koKR) localization strings for the update. This ensures that players using the Korean client can see accurate and clear translations for the new features and debuff filter settings without any untranslated English text.

How was it tested?

Tested in-game on the live retail client. Verified that all modified Lua localization strings load correctly without causing any Lua errors or interface script conflicts.

Checklist

• New settings default OFF (no behavior change without opt-in)
• Zero cost while disabled: no events registered, no polling, no hooks doing work, no frames built
• Cheap while enabled: event-driven (no polling, no timer-based logic, no per-frame allocations)
• No writes onto Blizzard-owned frames (weak-table pattern used); HookScript/hooksecurefunc only, never SetScript on Blizzard frames
• Tested in-game on live; no version gates or pre-Midnight APIs added