feat(post-form): native datetime-local picker + require date client-side

The stock Grav `datetime` field template is deprecated and falls back to a
plain text box, so `type: datetime` + `default: now` rendered a raw input
showing the literal word "now" — unusable. Add a theme override at
templates/forms/fields/datetime/datetime.html.twig that renders a native
<input type="datetime-local"> (real calendar+clock, great on mobile), drop
the `default: now`, and prefill the current local time from post-form.js.

Also add `date` to the existing client-side validator. Together with the
picker (which can't hold an invalid value) this stops a bad/empty date from
round-tripping to the server — which was the trigger that made Grav re-render
the managed FilePond field from the session flash as filename-only inputs and
resurrect a photo the user had removed. Grav still reformats the submitted
value to the blueprint `format: 'Y-m-d H:i'` on save, so stored dates and
folder slugs are unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

themes/intotheeast/js/src/post-form.js

@@ -433,11 +433,29 @@ function initGeo() {
  * Replaces the template's inline validator. Reads the EasyMDE-synced content
  * value (initEditor keeps the textarea current) and shows per-field messages.
  */
+// Current local wall-clock time as the value a datetime-local input expects
+// ("YYYY-MM-DDTHH:MM"). Uses the browser's timezone — the server has no idea
+// where the traveller is — and strips seconds so the value round-trips cleanly.
+function localNowDatetime() {
+    var d = new Date();
+    d.setSeconds(0, 0);
+    d.setMinutes(d.getMinutes() - d.getTimezoneOffset());
+    return d.toISOString().slice(0, 16);
+}
+
 function initValidation() {
-    var REQUIRED = { title: 'Title', content: 'Content' };
+    var REQUIRED = { title: 'Title', date: 'Date & time', content: 'Content' };
     var form = document.querySelector('form[name="new-entry"]');
     if (!form) return;
 
+    // Prefill the date/time picker with "now" (local) unless draft restore
+    // already put a value there. initDraft runs before initValidation in boot(),
+    // so an empty field here means there was no saved draft date to keep.
+    var dateEl = field('date');
+    if (dateEl && !String(dateEl.value).trim()) {
+        dateEl.value = localNowDatetime();
+    }
+
     function clearErrors() {
         form.querySelectorAll('.field-error').forEach(function (el) { el.remove(); });
         form.querySelectorAll('.field-invalid').forEach(function (el) { el.classList.remove('field-invalid'); });