Introduce a simple stimulus controller for the magic link form

which avoids the double-submit problem from:

- https://app.fizzy.do/5986089/cards/2980
- https://app.fizzy.do/5986089/cards/2771

app/javascript/controllers/magic_link_controller.js

@@ -0,0 +1,19 @@
+import { Controller } from "@hotwired/stimulus"
+import { onNextEventLoopTick } from "helpers/timing_helpers"
+
+export default class extends Controller {
+  static targets = [ "input" ]
+
+  submit(event) {
+    onNextEventLoopTick(() => {
+      this.inputTarget.disabled = true
+    })
+  }
+
+  paste(event) {
+    onNextEventLoopTick(() => {
+      this.element.submit()
+      this.inputTarget.disabled = true
+    })
+  }
+}