Fix potential double form submission in signup tracking

[leogdion]

Issue

The form submission logic in index.ts:20-32 has both a callback AND a setTimeout, which could result in duplicate submissions if the callback executes quickly.

Current code:

plausible.trackEvent("signup", {
  callback: () => {
    formElement.submit();  // Submit #1
  },
  props,
});
setTimeout(() => {
  formElement.submit();    // Submit #2 (after 500ms)
}, 500);

Impact

Users might receive duplicate emails or create duplicate records in the system.

Recommendation

Remove the redundant setTimeout or add a flag to prevent double submission:

let submitted = false;
plausible.trackEvent("signup", {
  callback: () => {
    if (!submitted) {
      submitted = true;
      formElement.submit();
    }
  },
  props,
});
setTimeout(() => {
  if (!submitted) {
    submitted = true;
    formElement.submit();
  }
}, 500);

This ensures the form is only submitted once, either when the tracking callback fires or after 500ms timeout.