fix(security): fix login AND logic to OR, add signup input validation, separate OTP rate limit keys

backend/auth/signup.php

@@ -12,6 +12,24 @@ $gender      = filterRequest("gender");
 $birthdate   = filterRequest("birthdate");
 $site        = filterRequest("site");
 
+// --- Input Validation ---
+if (empty($phone) || strlen(preg_replace('/\D+/', '', $phone)) < 8) {
+    jsonError("Valid phone number is required.");
+    exit;
+}
+if (!empty($email) && !filter_var($email, FILTER_VALIDATE_EMAIL)) {
+    jsonError("Valid email address is required.");
+    exit;
+}
+if (empty($password) || strlen($password) < 6) {
+    jsonError("Password must be at least 6 characters.");
+    exit;
+}
+if (empty($first_name) || empty($last_name)) {
+    jsonError("First name and last name are required.");
+    exit;
+}
+
 // تشفير البيانات الحساسة
 $phone       = $encryptionHelper->encryptData($phone);
 $email       = $encryptionHelper->encryptData($email);