feat: add duplicate email detection via auth hook with fallback

- Add before-user-created hook function for server-side duplicate email detection
- Implement fallback detection using identities array check (Supabase limitation)
- Update signUpWithPassword to detect duplicate emails via hook errors or empty identities
- Add error handling in login page to show duplicate email errors and auto-switch to login mode
- Add auth hook setup documentation and test scripts
- Add password reset and update password flows
- Add email templates for signup confirmation and password reset

scripts/test-signup-direct.ts

@@ -0,0 +1,47 @@
+#!/usr/bin/env tsx
+/**
+ * Test Signup Direct
+ * Test wat Supabase teruggeeft bij duplicate email signup
+ */
+
+import { config } from 'dotenv'
+import { createClient } from '@supabase/supabase-js'
+
+config({ path: '.env.local' })
+
+const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL!
+const supabaseAnonKey = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY!
+
+const supabase = createClient(supabaseUrl, supabaseAnonKey)
+
+async function testSignup() {
+  console.log('🧪 Testing Direct Signup with Existing Email\n')
+  console.log('URL:', supabaseUrl)
+  console.log('Testing with email: colin@ikbenlit.nl\n')
+
+  const { data, error } = await supabase.auth.signUp({
+    email: 'colin@ikbenlit.nl',
+    password: 'TestPassword123!',
+    options: {
+      emailRedirectTo: `http://localhost:3000/auth/callback`
+    }
+  })
+
+  console.log('📊 Response:')
+  console.log('Data:', JSON.stringify(data, null, 2))
+  console.log('\nError:', JSON.stringify(error, null, 2))
+
+  console.log('\n📝 Analysis:')
+  if (error) {
+    console.log('✅ Hook is working! Error received:', error.message)
+  } else if (data.user && data.session) {
+    console.log('⚠️  User created with session (email confirmation disabled)')
+  } else if (data.user) {
+    console.log('⚠️  User object returned without session')
+  } else {
+    console.log('❌ No error but no user - Hook might not be working')
+    console.log('   This is the "silent fail" scenario')
+  }
+}
+
+testSignup().catch(console.error)