### Added
- **In-Game Layout Editor:** Complete visual GUI editor for custom shop layouts — no config editing required!
- Open with `/endex shop editor <shop-id>` (e.g., `/endex shop editor main`)
- **5 Editor Modes:** Place Category, Place Decoration, Place Button, Edit Slot, Remove Slot
- **Custom Items Support:** Add any material as decoration or custom items with personalized names and lores
- **Visual Preview:** See changes in real-time before saving
- **Right-Click Editing:** Right-click any placed item to customize its display name and lore
- **Chained Prompts:** Edit name then lore in sequence via chat input
- **State Preservation:** Navigate between editor dialogs without losing unsaved changes
- **One-Click Save:** Save button writes layout directly to shop config file

- **Custom Category Icons:** Categories can now have fully customized display names and lores
- Set via layout editor or directly in shop config
- Custom names/lores display correctly in `/market` player view

### Technical
- `TITLE_PREFIX = "§4§l⚙ "` distinguishes editor GUIs from player shop GUIs
- `reopenLayoutEditor()` preserves `tempLayout` and `unsavedChanges` state across dialogs
- Mode priority system ensures Edit/Remove modes work on existing items
- Chained text input via `pendingInputType` for name → lore flow