feat(click casting): optionally target the unit you click-cast on

[Krathe82]

Summary

Adds a "target on cast" behaviour so click-casting a spell on a frame can also set that unit as your target (lab features #410, #15).

• Global toggle "Target unit when click-casting" in the Click Casting profiles panel (off by default).
• Per-binding override under Advanced → Macro Options. Three-way: inherit (default) / On / Off — an explicit override wins over the global, while leaving it untouched keeps following the global toggle.
• Implemented by appending /target [@mouseover,exists] mouseover to the generated cast macro. The mouseover gate means a frame click targets that unit, while a target-fallback cast (nothing hovered) leaves your current target alone. Works in combat (secure macro).
• Covers the single and combined (friendly+hostile) macro paths; the combined path targets if any contributing binding opts in.
• Applies to spell/item casts only; custom macros and the target/focus/menu/assist special actions are untouched.

Test plan

• Global toggle on → click-cast a heal on a frame targets that unit; mouseover-cast (no frame) leaves target unchanged.
• Per-binding On with global off → only that binding targets.
• Per-binding Off with global on → that binding doesn't target.
• Untouched per-binding follows the global toggle after changing it.
• Works in combat; no Lua errors; custom-macro and special-action binds unaffected.