Fix Supabase linter warnings and backend validation

src/components/auth/AuthModal.tsx

@@ -14,6 +14,7 @@ import { useCaptchaBypass } from '@/hooks/useCaptchaBypass';
 import { MFAChallenge } from './MFAChallenge';
 import { verifyMfaUpgrade } from '@/lib/authService';
 import { setAuthMethod } from '@/lib/sessionFlags';
+import { validateEmailNotDisposable } from '@/lib/emailValidation';
 
 interface AuthModalProps {
   open: boolean;
@@ -178,6 +179,20 @@ export function AuthModal({ open, onOpenChange, defaultTab = 'signin' }: AuthMod
     setCaptchaToken(null);
 
     try {
+      // Validate email is not disposable
+      const emailValidation = await validateEmailNotDisposable(formData.email);
+
+      if (!emailValidation.valid) {
+        toast({
+          variant: "destructive",
+          title: "Invalid Email",
+          description: emailValidation.reason || "Please use a permanent email address"
+        });
+        setCaptchaKey(prev => prev + 1);
+        setLoading(false);
+        return;
+      }
+
       const signUpOptions: any = {
         email: formData.email,
         password: formData.password,