Add Sign Up functionality to desktop app (#5244)

# Description of Changes
Adds Sign Up with email to desktop app. SSO sign up will come in a
future PR.

frontend/src/desktop/components/SetupWizard/index.tsx

@@ -2,16 +2,20 @@ import React, { useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { DesktopAuthLayout } from '@app/components/SetupWizard/DesktopAuthLayout';
 import { SaaSLoginScreen } from '@app/components/SetupWizard/SaaSLoginScreen';
+import { SaaSSignupScreen } from '@app/components/SetupWizard/SaaSSignupScreen';
 import { ServerSelectionScreen } from '@app/components/SetupWizard/ServerSelectionScreen';
 import { SelfHostedLoginScreen } from '@app/components/SetupWizard/SelfHostedLoginScreen';
 import { ServerConfig, connectionModeService } from '@app/services/connectionModeService';
 import { authService, UserInfo } from '@app/services/authService';
 import { tauriBackendService } from '@app/services/tauriBackendService';
 import { STIRLING_SAAS_URL } from '@desktop/constants/connection';
+import { listen } from '@tauri-apps/api/event';
+import { useEffect } from 'react';
 import '@app/routes/authShared/auth.css';
 
 enum SetupStep {
   SaaSLogin,
+  SaaSSignup,
   ServerSelection,
   SelfHostedLogin,
 }
@@ -80,6 +84,16 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
     setActiveStep(SetupStep.ServerSelection);
   };
 
+  const handleSwitchToSignup = () => {
+    setError(null);
+    setActiveStep(SetupStep.SaaSSignup);
+  };
+
+  const handleSwitchToLogin = () => {
+    setError(null);
+    setActiveStep(SetupStep.SaaSLogin);
+  };
+
   const handleServerSelection = (config: ServerConfig) => {
     setServerConfig(config);
     setError(null);
@@ -128,6 +142,48 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
     }
   };
 
+  useEffect(() => {
+    const unsubscribePromise = listen<string>('deep-link', async (event) => {
+      const url = event.payload;
+      if (!url) return;
+
+      try {
+        const parsed = new URL(url);
+
+        // Supabase sends tokens in the URL hash
+        const hash = parsed.hash.replace(/^#/, '');
+        const params = new URLSearchParams(hash);
+        const accessToken = params.get('access_token');
+        const type = params.get('type') || parsed.searchParams.get('type');
+
+        if (!type || (type !== 'signup' && type !== 'recovery' && type !== 'magiclink')) {
+          return;
+        }
+
+        if (!accessToken) {
+          console.error('[SetupWizard] Deep link missing access_token');
+          return;
+        }
+
+        setLoading(true);
+        setError(null);
+
+        await authService.completeSupabaseSession(accessToken, serverConfig?.url || STIRLING_SAAS_URL);
+        await connectionModeService.switchToSaaS(serverConfig?.url || STIRLING_SAAS_URL);
+        tauriBackendService.startBackend().catch(console.error);
+        onComplete();
+      } catch (err) {
+        console.error('[SetupWizard] Failed to handle deep link', err);
+        setError(err instanceof Error ? err.message : 'Failed to complete signup');
+        setLoading(false);
+      }
+    });
+
+    return () => {
+      void unsubscribePromise.then((unsub) => unsub());
+    };
+  }, [onComplete, serverConfig?.url]);
+
   const handleBack = () => {
     setError(null);
     if (activeStep === SetupStep.SelfHostedLogin) {
@@ -135,6 +191,8 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
     } else if (activeStep === SetupStep.ServerSelection) {
       setActiveStep(SetupStep.SaaSLogin);
       setServerConfig({ url: STIRLING_SAAS_URL });
+    } else if (activeStep === SetupStep.SaaSSignup) {
+      setActiveStep(SetupStep.SaaSLogin);
     }
   };
 
@@ -147,11 +205,21 @@ export const SetupWizard: React.FC<SetupWizardProps> = ({ onComplete }) => {
           onLogin={handleSaaSLogin}
           onOAuthSuccess={handleSaaSLoginOAuth}
           onSelfHostedClick={handleSelfHostedClick}
+          onSwitchToSignup={handleSwitchToSignup}
           loading={loading}
           error={error}
         />
       )}
 
+      {activeStep === SetupStep.SaaSSignup && (
+        <SaaSSignupScreen
+          loading={loading}
+          error={error}
+          onLogin={handleSaaSLogin}
+          onSwitchToLogin={handleSwitchToLogin}
+        />
+      )}
+
       {activeStep === SetupStep.ServerSelection && (
         <ServerSelectionScreen
           onSelect={handleServerSelection}