Hide Known

What I fixed:

• Lua error: Removed registration of the unsupported PET_TRAINER_SHOW event.
• Warlock demon grimoires: Added vendor tooltip detection for items marked Already Known or Already Learned.
• Vendor interface: Known items are now dimmed rather than removed, avoiding incorrect merchant slot indexing.
• Commands: Added /hk vendor to toggle vendor filtering.
• Saved settings: Retained the existing configuration system.

Important: The new vendor detection has not been tested in-game. It depends on WoW Forever exposing the appropriate tooltip text.

Also, this version dims known grimoires rather than completely hiding them. Once we verify detection works, we can work on removing known entries from the displayed vendor list.

If the grimoires still aren't detected, tell me whether their tooltips actually say Already Known or use different wording.