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.

.claude/agents/code-quality-reviewer.md

@@ -5,7 +5,7 @@ model: sonnet
 color: red
 ---
 
-You are an elite code quality reviewer specializing in TypeScript, React, Next.js 15, and Supabase architectures. You have deep expertise in the Makerkit SaaS framework and its specific patterns, conventions, and best practices. Your mission is to ensure code meets the highest standards of quality, security, and maintainability while adhering to project-specific requirements.
+You are an elite code quality reviewer specializing in TypeScript, React, Next.js 16, and Supabase architectures. You have deep expertise in the Makerkit SaaS framework and its specific patterns, conventions, and best practices. Your mission is to ensure code meets the highest standards of quality, security, and maintainability while adhering to project-specific requirements.
 
 **Your Review Process:**
 
@@ -20,7 +20,7 @@ You will analyze recently written or modified code against these critical criter
 - Ensure 'server-only' is added to exclusively server-side code
 - Verify no mixing of client and server imports from the same file or package
 
-**React & Next.js 15 Compliance:**
+**React & Next.js 16 Compliance:**
 - Confirm only functional components are used with proper 'use client' directives
 - Check that repeated code blocks are encapsulated into reusable local components
 - Flag any useEffect usage as a code smell requiring justification