feat: add extra hovercast options

[asdfractal]

What does this PR do?

• Add option to enable/disable binding based on content type: solo/party/raid/pvp. Default: All
• Add option to enable binding on frames only, unit only, or both. Default: Frames, if someone had this toggle checked, it will be set to units.

How was it tested?

PTR, follower with /euidev and in combat. Live in raid.
"cast on" tested for both click and key bindings.

Screenshots

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, works on live retail; no load errors on the 12.1 PTR client