feat: enhance authentication UX with password visibility toggle and better error messages

Added comprehensive improvements to the login and authentication flow:

**UI Improvements:**
- Add password visibility toggle (Eye/EyeOff icons) for password fields
- Improve error message consistency with Dutch translations
- Fix syntax error in login page try-catch block

**Error Handling:**
- Add user-friendly error messages for invalid credentials
- Add specific error codes: invalid_credentials, email_not_confirmed
- Improve error message for non-existent accounts during login
- Handle duplicate email detection during signup with auto-switch to login mode

**Middleware:**
- Add /reset-password and /update-password to public routes
- Fix redirect issue preventing access to password reset flow

**Password Reset Flow:**
- Verify password reset works for magic link users (can set initial password)
- Ensure existing password users can reset their password
- Both flows use the same update mechanism via Supabase

**Documentation:**
- Add comprehensive release notes in docs/RELEASE_AUTH_IMPROVEMENTS.md

All changes maintain backward compatibility with existing magic link users.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

middleware.ts

@@ -46,6 +46,8 @@ export async function middleware(request: NextRequest) {
   const publicRoutes = [
     '/',
     '/login',
+    '/reset-password',
+    '/update-password',
     '/auth/callback',
     '/contact',
     '/api/leads',