Add keyboard shortcut "N" to open new task modal

File: client/src/pages/Dashboard.jsx

Power users love keyboard shortcuts!

Fix:
useEffect(() => {
  const handler = (e) => {
    if (e.key === "n" && !e.target.matches("input,textarea"))
      setModalOpen(true)
  }
  window.addEventListener("keydown", handler)
  return () => window.removeEventListener("keydown", handler)
}, [])
~8 lines!