Design a Notification Center with Smart Grouping and Priority Levels

Design a notification center system for [PLATFORM TYPE, e.g., SaaS dashboard, mobile app, e-commerce site] that serves [TARGET USERS]. The application handles approximately [VOLUME, e.g., 10-50] notifications per user per day across [NUMBER] distinct notification categories. Provide a complete design specification: 1. **Notification Anatomy**: Define the structure of a single notification card, including: icon/avatar, title (max characters), body text (max characters), timestamp format (relative vs. absolute), action buttons (max 2), and unread/read visual indicator. 2. **Priority System**: Establish 3 priority tiers (e.g., Critical, Standard, Informational). For each tier, define visual differentiation (color, iconography, position), sound/vibration behavior on mobile, and persistence rules (auto-dismiss timing or manual dismissal). 3. **Grouping & Stacking**: Describe how similar notifications collapse (e.g., '5 people liked your post'). Define the threshold for grouping, expanded vs. collapsed states, and the logic for ungrouping. 4. **Notification Panel Layout**: Specify the panel's entry point (bell icon with badge counter), panel dimensions, scroll behavior, filtering tabs (e.g., All, Unread, Mentions), and the 'Mark all as read' interaction. 5. **Empty & Edge States**: Design for zero notifications, error loading notifications, and notification overflow (100+ unread). Provide copy and illustration guidance. 6. **User Preferences**: Outline a notification settings page where users can toggle channels (in-app, email, push) per category, set quiet hours, and adjust frequency. 7. **Motion & Timing**: Describe entry animations, exit animations, and toast notification behavior for real-time alerts. Format as a design system-ready specification document.