chore: document local WSL setup fixes

backend/internal/service/redis_service.go

@@ -78,6 +78,9 @@ func (s *RedisService) Ping(ctx context.Context) error {
 
 // StoreVerificationCode saves the SMS verification code with a 3-minute expiration
 func (s *RedisService) StoreVerificationCode(phone, code string) error {
+	if s == nil || s.Client == nil {
+		return os.ErrInvalid
+	}
 	// Key format: "sms_verify:01012345678"
 	key := "sms_verify:" + phone
 	expiration := 3 * time.Minute
@@ -87,6 +90,9 @@ func (s *RedisService) StoreVerificationCode(phone, code string) error {
 
 // GetVerificationCode retrieves the SMS verification code
 func (s *RedisService) GetVerificationCode(phone string) (string, error) {
+	if s == nil || s.Client == nil {
+		return "", os.ErrInvalid
+	}
 	key := "sms_verify:" + phone
 	code, err := s.Client.Get(ctx, key).Result()
 	if err == redis.Nil {
@@ -100,17 +106,26 @@ func (s *RedisService) GetVerificationCode(phone string) (string, error) {
 
 // DeleteVerificationCode removes the verification code after successful verification
 func (s *RedisService) DeleteVerificationCode(phone string) error {
+	if s == nil || s.Client == nil {
+		return os.ErrInvalid
+	}
 	key := "sms_verify:" + phone
 	return s.Client.Del(ctx, key).Err()
 }
 
 // Set stores a key-value pair with expiration
 func (s *RedisService) Set(key string, value string, expiration time.Duration) error {
+	if s == nil || s.Client == nil {
+		return os.ErrInvalid
+	}
 	return s.Client.Set(ctx, key, value, expiration).Err()
 }
 
 // Get retrieves a value by key
 func (s *RedisService) Get(key string) (string, error) {
+	if s == nil || s.Client == nil {
+		return "", os.ErrInvalid
+	}
 	val, err := s.Client.Get(ctx, key).Result()
 	if err == redis.Nil {
 		return "", nil
@@ -120,6 +135,9 @@ func (s *RedisService) Get(key string) (string, error) {
 
 // Delete removes a key
 func (s *RedisService) Delete(key string) error {
+	if s == nil || s.Client == nil {
+		return os.ErrInvalid
+	}
 	return s.Client.Del(ctx, key).Err()
 }