fix: replace crypto/md5 with crypto/sha256 for IP hashing

backend/handlers/bookings/admin_reserve.go

@@ -2,7 +2,7 @@ package bookings
 
 import (
 	"context"
-	"crypto/md5"
+	"crypto/sha256"
 	"crussell/clock"
 	"crussell/db"
 	"crussell/handlers/scheduling"
@@ -152,7 +152,7 @@ func AdminReserveSlotHandler(w http.ResponseWriter, r *http.Request) {
 			ip = r.RemoteAddr
 		}
 	}
-	ipHash := fmt.Sprintf("%x", md5.Sum([]byte(ip)))[:8]
+	ipHash := fmt.Sprintf("%x", sha256.Sum256([]byte(ip)))[:8]
 	if _, delErr := db.Conn.Exec(r.Context(), `
 		DELETE FROM time_blockers
 		WHERE (description LIKE 'RESERVATION:admin:%' AND created_by = $1)