chore: drop unused SWR hooks and dependency

useSchools, useFilters, useMetrics and useSchoolDetails were imported by
nothing and were the only consumers of swr. All data fetching goes through
lib/api.ts on the server.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

nextjs-app/package.json

@@ -26,7 +26,6 @@
     "react-chartjs-2": "^5.3.1",
     "react-dom": "^19.2.4",
     "react-leaflet": "^5.0.0",
-    "swr": "^2.4.0",
     "typescript": "^5.9.3",
     "zod": "^4.3.6"
   },