fix: translate the DateTime filter term to StartDateTime for the events API

loadEventData() builds the API URL straight from the filter form's terms
and translated only one attribute name, Monitor to MonitorId.  But
montagereview.php expresses both of its time bounds as the DateTime
pseudo-attribute, which is a filter-engine concept rather than an Events
column: Filter.php resolves 'DateTime' and 'StartDateTime' to the same
E.StartDateTime, and groups them together everywhere else it special-cases
date attributes.

The API takes real column names and silently ignores a term it cannot
resolve, so the two bounds were dropped and the view got page one of every
event ever recorded instead of the requested window.  Both requests return
200, which is why nothing surfaced.  Measured against a live install for
the 2026-08-28 00:00:00 to 01:00:00 window:

  DateTime      >=/<=  ->  757 rows, first event 2025-04-26 16:29:55
  StartDateTime >=/<=  ->  300 rows, 00:00:59 to 00:59:59

Translate DateTime the same way Monitor is already translated.  Rewriting
the form element is safe for the PHP path too, since Filter.php treats the
two names identically.

web/skins/classic/views/js/montagereview.js

@@ -1317,6 +1317,12 @@ function loadEventData(e) {
           const op = this.form.elements[op_name];
           if (attr) {
             if (attr.value==='Monitor') attr.value='MonitorId';
+            // DateTime is a filter-engine pseudo-attribute, not an Events
+            // column: Filter.php resolves 'DateTime' and 'StartDateTime' to the
+            // same E.StartDateTime.  The API takes column names, and silently
+            // ignores a term it cannot resolve rather than erroring, so leaving
+            // it as DateTime returns every event ever instead of the window.
+            if (attr.value==='DateTime') attr.value='StartDateTime';
             let urlVal = val;
             // Normalize date/time values to YYYY-MM-DD HH:mm:ss for the API URL.
             // Locale formats using / as separator break the URL path.