fix(invitations): Support both platform and staff invitation types

- Update useInvitationDetails to try platform tenant invitation first,
  then fall back to staff invitation
- Update useAcceptInvitation to handle both invitation types
- Update useDeclineInvitation to handle both invitation types
- Pass invitation type from AcceptInvitePage to mutations

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

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

frontend/src/pages/AcceptInvitePage.tsx

@@ -68,6 +68,7 @@ const AcceptInvitePage: React.FC = () => {
         firstName: firstName.trim(),
         lastName: lastName.trim(),
         password,
+        invitationType: invitation?.invitation_type,
       });
 
       // Set auth tokens and redirect to dashboard
@@ -89,7 +90,7 @@ const AcceptInvitePage: React.FC = () => {
     }
 
     try {
-      await declineInvitationMutation.mutateAsync(token!);
+      await declineInvitationMutation.mutateAsync({ token: token!, invitationType: invitation?.invitation_type });
       setDeclined(true);
     } catch (err: any) {
       setFormError(err.response?.data?.error || t('acceptInvite.declineFailed', 'Failed to decline invitation'));