- Add menu_layout_cache.py for CABINET_MENU_LAYOUT in-process cache
- Add admin_menu_layout.py routes (GET/PUT/POST reset) with merged view
- Rewrite _build_cabinet_main_menu_keyboard to use cached row layout
- Support custom URL buttons with style, emoji, labels, enabled toggle
- Atomic dual-key DB writes for layout + button styles
- Add language button to default layout and DEFAULT_BUTTON_STYLES
- Pydantic validation with Literal types, max_length, duplicate ID checks
- Register routes and cache loading in bot startup