feat: add Healing Radial for quick party member targeting

[DKulan]

A radial menu designed for healers to quickly target party members while in Mouse Look mode. Hold a mouse button to display the radial, flick toward your target, and release to cast.

Features:

• Displays party members as slices arranged around screen center
• Role-based positioning: Tank at 12 o'clock, Healer at 7 o'clock, DPS fill remaining positions
• Cast-on-release behavior prevents accidental spell casts
• Shows health bars, health percentages, player names, and role icons
• Configurable visual settings (colors, slice size, fade duration)
• OnUpdate polling for reliable mouse release detection
• Supports modifier keys (Shift, Ctrl, Alt) for additional bindings

Configuration:

• New "Healing Radial" section in addon settings
• Toggle to enable/disable the feature
• Visual customization options for health bars, names, and colors

[sampconrad]

I'll just copy what we discussed on Discord here so we can have a more focused discussion regarding the feature.

One suggestion, if I may. Instead of having a plain box, maybe have a circular portrait of the party members with the bar underneath or a coloured percentage value representing their health. This could even allow them to select between a 2D portrait of their character, class, or role icons for the foreground. Similar to what other addons do:

The end result would be something like this:

It would make it much easier for the user to tell the party members apart at a quick glance in the midst of combat compared to the screenshot you provided, in which the boxes are too similar to one another.

You mentioned on Discord you'd be refining this up a bit in the coming days, so I'll hold off on merging until then. But I'll 100% be approving this PR! Thanks again for the awesome work!