How do i set unique index to username checking

 if (url.pathname === '/auth/check-username' && request.method === 'POST') {
      const { username } = await request.json();

      const normalizedUsername = (username || '').toLowerCase().trim();

      if (!normalizedUsername || !/^[a-z0-9_.]{3,16}$/.test(normalizedUsername)) {
        return new Response(JSON.stringify({
          available: false,
          error: 'Username muss 3–16 Zeichen [a-z0-9_\\.] haben'
        }), {
          status: 400,
          headers: { 'Content-Type': 'application/json', ...CORS_HEADERS }
        });
      }

      const { data, error } = await supabase
          .from('profiles')
          .select('id')
          .ilike('username', normalizedUsername)
          .maybeSingle();

      console.log('🔍 Username Check:', {
        input: username,
        normalized: normalizedUsername,
        found: !!data,
        error
      });

      return new Response(JSON.stringify({
        available: !data,
        username: normalizedUsername
      }), {
        status: 200,
        headers: { 'Content-Type': 'application/json', ...CORS_HEADERS }
      });
    }