fix: admin role change, logo access, magic link validation, login help

- Add updateTeamMemberRole mutation for admins to change team member roles
- Allow any team member (not just lead) to change project logo
- Add visible "Add logo"/"Change" label under logo for discoverability
- Pre-check email existence before sending magic link (show error)
- Add "forgot which email" contact link on login page

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/(auth)/login/page.tsx

@@ -69,6 +69,19 @@ export default function LoginPage() {
     setError(null)
 
     try {
+      // Pre-check: does this email exist?
+      const checkRes = await fetch('/api/auth/check-email', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ email }),
+      })
+      const checkData = await checkRes.json()
+      if (!checkData.exists) {
+        setError('No account found with this email address. Please check the email you used to sign up, or contact the administrator.')
+        setIsLoading(false)
+        return
+      }
+
       // Get CSRF token first
       const csrfRes = await fetch('/api/auth/csrf')
       const { csrfToken } = await csrfRes.json()
@@ -300,6 +313,12 @@ export default function LoginPage() {
               </>
             )}
           </button>
+          <p className="mt-3 text-xs text-muted-foreground/70 text-center">
+            Don&apos;t remember which email you used?{' '}
+            <a href="mailto:contact@monaco-opc.com" className="underline hover:text-primary transition-colors">
+              Contact the MOPC team
+            </a>
+          </p>
         </div>
       </CardContent>
     </Card>