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

backend/handlers/bookings/overlap_test.go

@@ -5,7 +5,7 @@ package bookings
 import (
 	"bytes"
 	"context"
-	"crypto/md5"
+	"crypto/sha256"
 	"encoding/json"
 	"fmt"
 	"net/http"
@@ -1938,7 +1938,7 @@ func TestReserveSlot_CleansUpAnonReservation(t *testing.T) {
 
 	// Set a known IP that the test request will use
 	testIP := "192.0.2.1"
-	ipHash := fmt.Sprintf("%x", md5.Sum([]byte(testIP)))[:8]
+	ipHash := fmt.Sprintf("%x", sha256.Sum256([]byte(testIP)))[:8]
 
 	// Create an anonymous reservation (created_by = NULL) matching this IP hash
 	var blockerID string
@@ -2139,7 +2139,7 @@ func TestAdminReserveSlot_CleansUpAnonReservation(t *testing.T) {
 
 	future := weekdayTime(time.Monday, 10)
 	testIP := "192.0.2.2"
-	ipHash := fmt.Sprintf("%x", md5.Sum([]byte(testIP)))[:8]
+	ipHash := fmt.Sprintf("%x", sha256.Sum256([]byte(testIP)))[:8]
 
 	// Create an anonymous reservation matching this IP
 	var blockerID string