Rework dashboard UI premium

Refactor admin dashboard to a premium, design-system aligned layout. Convert stat cards to clickable drill-downs with proper filters and updated navigation, add responsive styling, and refresh table/sidebar visuals. Includes updated Dashboard.tsx structure to support drill-down actions.

X-Lovable-Edit-ID: edt-43ba1210-1211-4238-aa4f-27ad3a431548

Author: lovable-dev[bot]