[feat](trx-frontend-http): add interleave time for overlapping TimeSpan entries

When multiple time-span entries are active simultaneously, the scheduler
now cycles through them by slot: slot = floor(utc_min / interleave_min) % count.
The interleave_min field is optional (null disables, first match wins).

UI: "Interleave time (min)" number input in the TimeSpan section with a
hint explaining the behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/scheduler.js

@@ -195,6 +195,13 @@
       renderBookmarkSelect("scheduler-gl-night", null);
     }
 
+    // Interleave input
+    const ilEl = document.getElementById("scheduler-ts-interleave");
+    if (ilEl) {
+      const il = currentConfig && currentConfig.interleave_min;
+      ilEl.value = il ? il : "";
+    }
+
     // TimeSpan entries
     renderTimespanEntries();
 
@@ -374,6 +381,8 @@
     } else if (mode === "time_span") {
       config.entries =
         currentConfig && currentConfig.entries ? currentConfig.entries : [];
+      const ilVal = parseInt(document.getElementById("scheduler-ts-interleave").value, 10);
+      config.interleave_min = isNaN(ilVal) || ilVal <= 0 ? null : ilVal;
     }
 
     const btn = document.getElementById("scheduler-save-btn");