Fix double /api prefix in fetchAccesses by using ENDPOINTS constant

fetchAccesses was passing the hardcoded absolute path /api/dashboard/accesses
to get(), which prepends BASE_URL (/api), producing /api/api/dashboard/accesses.
Added ENDPOINTS.dashboardAccesses and switched to use it, consistent with every
other function in dashboard.ts.

frontend/src/api/endpoints.ts

@@ -30,6 +30,7 @@ export const ENDPOINTS = {
   dashboardStatus: "/dashboard/status",
   dashboardBans: "/dashboard/bans",
   dashboardBansByCountry: "/dashboard/bans/by-country",
+  dashboardAccesses: "/dashboard/accesses",
 
   // -------------------------------------------------------------------------
   // Jails