chore: improve invitation flow, update project dependencies and documentation for Next.js 16 (#408)

* chore: update project dependencies and documentation for Next.js 16

- Upgraded Next.js from version 15 to 16 across various documentation files and components.
- Updated references to Next.js 16 in AGENTS.md and CLAUDE.md for consistency.
- Incremented application version to 2.21.0 in package.json.
- Refactored identity setup components to improve user experience and added confirmation dialogs for authentication methods.
- Enhanced invitation flow with new logic for handling user redirection and token generation.

* refactor: streamline invitation flow in e2e tests

- Simplified the invitation flow test by using a predefined email instead of generating a random one.
- Removed unnecessary steps such as clearing cookies and reloading the page before user sign-up.
- Enhanced clarity by eliminating commented-out code related to identity verification and user membership checks.

* refactor: improve code readability in IdentitiesPage and UpdatePasswordForm components

- Enhanced formatting of JSX elements in IdentitiesPage and UpdatePasswordForm for better readability.
- Adjusted indentation and line breaks to maintain consistent coding style across components.

* refactor: enhance LinkAccountsList component with user redirection logic

- Updated the LinkAccountsList component to include a redirectToPath option in the useLinkIdentityWithProvider hook for improved user experience.
- Removed redundant user hook declaration to streamline the code structure.

* refactor: update account setup logic in JoinTeamAccountPage

- Introduced a check for email-only authentication support to streamline account setup requirements.
- Adjusted the conditions for determining if a new account should set up additional authentication methods, enhancing user experience for new users.

apps/web/app/join/page.tsx

@@ -24,6 +24,7 @@ interface JoinTeamAccountPageProps {
     invite_token?: string;
     type?: 'invite' | 'magic-link';
     email?: string;
+    is_new_user?: string;
   }>;
 }
 
@@ -131,16 +132,18 @@ async function JoinTeamAccountPage(props: JoinTeamAccountPageProps) {
 
   // Determine if we should show the account setup step (Step 2)
   // Decision logic:
-  // 1. Only show for new accounts (linkType === 'invite')
-  // 2. Only if we have auth options available (password OR OAuth)
+  // 1. Only show for new accounts (is_new_user === 'true' or linkType === 'invite')
+  // 2. Only if we don't support email only auth (magic link or OTP)
   // 3. Users can always skip and set up auth later in account settings
   const linkType = searchParams.type;
-  const supportsPasswordSignUp = authConfig.providers.password;
-  const supportsOAuthProviders = authConfig.providers.oAuth.length > 0;
-  const isNewAccount = linkType === 'invite';
+  const isNewUserParam = searchParams.is_new_user === 'true';
 
-  const shouldSetupAccount =
-    isNewAccount && (supportsPasswordSignUp || supportsOAuthProviders);
+  // if the app supports email only auth, we don't need to setup any other auth methods. In all other cases (passowrd, oauth), we need to setup at least one of them.
+  const supportsEmailOnlyAuth =
+    authConfig.providers.magicLink || authConfig.providers.otp;
+
+  const isNewAccount = isNewUserParam || linkType === 'invite';
+  const shouldSetupAccount = isNewAccount && !supportsEmailOnlyAuth;
 
   // Determine redirect destination after joining:
   // - If shouldSetupAccount: redirect to /identities with next param (Step 2)