feat: add geolocation fields to session and implement geo stats endpoint

- Added country, city, countryCode, latitude, and longitude fields to the Session model.
- Updated geoip service to fetch and store geolocation data based on user IP.
- Created a new admin endpoint to retrieve geolocation statistics, including user counts by country and city.
- Enhanced admin page to display geolocation statistics with expandable city details.
- Introduced caching for geolocation data to optimize performance.

apps/backend/prisma/migrations/20260610131124_add_session_geo_fields/migration.sql

@@ -0,0 +1,6 @@
+-- AlterTable
+ALTER TABLE "sessions" ADD COLUMN     "city" TEXT,
+ADD COLUMN     "country" TEXT,
+ADD COLUMN     "countryCode" TEXT,
+ADD COLUMN     "latitude" DOUBLE PRECISION,
+ADD COLUMN     "longitude" DOUBLE PRECISION;