Next.js Supabase V3 (#463)

Version 3 of the kit:
- Radix UI replaced with Base UI (using the Shadcn UI patterns)
- next-intl replaces react-i18next
- enhanceAction deprecated; usage moved to next-safe-action
- main layout now wrapped with [locale] path segment
- Teams only mode
- Layout updates
- Zod v4
- Next.js 16.2
- Typescript 6
- All other dependencies updated
- Removed deprecated Edge CSRF
- Dynamic Github Action runner

docs/troubleshooting/troubleshooting-authentication.mdoc

@@ -0,0 +1,24 @@
+---
+status: "published"
+title: 'Troubleshooting authentication issues in the Next.js Supabase kit'
+label: 'Authentication'
+order: 2
+description: 'Troubleshoot issues related to authentication in the Next.js Supabase SaaS kit'
+---
+
+
+## Supabase redirects to localhost instead of my website URL
+
+This is most likely an issue related to not having set up the Authentication URL in the Supabase settings as describe in [the going to production guide](../going-to-production/supabase);
+
+## Cannot Receive Emails from Supabase
+
+This issue may arise if you have not setup an SMTP provider from within Supabase.
+
+Supabase's own SMTP provider has low limits and low deliverability, therefore you must set up your own - and only use the default Supabase's one for testing purposes.
+
+## Cannot sign in with oAuth provider
+
+This is most likely a settings issues from within the Supabase dashboard or in the provider's settings.
+
+Please [read Supabase's documentation](https://supabase.com/docs/guides/auth/social-login) on how to set up third-party providers.