Tier 2: Face editor UI — app screen to configure/reorder device faces

[CodeCreatorManMike]

What to build

React Native screen in GravityApp that lets users:

• View their current 5 faces in a circular preview grid
• Add/remove face types (goal_arc, task_list, habit_heatmap, timer, study_progress)
• Drag-reorder faces (order = display priority)
• Edit face-specific config (e.g. goal for goal_arc, habit selection for heatmap)
• Save → PUT /device/layout → backend re-ranks and pushes LAYOUT_UPDATE via WebSocket

Circular face cards should mirror the round device aesthetic.