feat(frontend): add delete entry and update standby entry logic

frontend/src/lib/time-rules.js

@@ -207,20 +207,25 @@ export const generateStandbyEntries = (startDateStr, endDateStr) => {
     const start = new Date(Date.UTC(sy, sm - 1, sd, 12, 0, 0));
     const end = new Date(Date.UTC(ey, em - 1, ed, 12, 0, 0));
 
+    // Check if multi-day range
+    const isMultiDay = start.getTime() !== end.getTime();
+
     // Loop from start to end
     for (let d = new Date(start); d <= end; d.setDate(d.getDate() + 1)) {
         // Create local date object for holiday checking (using getFullYear/getMonth/getDate)
-        // We used UTC above for iteration safety, but need local context or consistent context for day checks.
-        // detectDayType uses local methods.
-        // Let's create a new Date object from the UTC components to treat it as "Local Noon" for checking.
-        // Actually, detectDayType uses .getDay() which is local.
-        // If we want consistency, we should ensure we are checking the "intended" date.
-        // The simplistic approach:
         const checkDate = new Date(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), 12, 0, 0);
 
         const dateStr = d.toISOString().split('T')[0];
         const dayType = detectDayType(checkDate);
-        const maxHours = getMaxStandbyHours(dayType);
+        let maxHours = getMaxStandbyHours(dayType);
+
+        // Standby Logic Update: First and Last day get half value if multi-day
+        // We compare timestamps of the current loop date 'd' with start/end
+        if (isMultiDay) {
+            if (d.getTime() === start.getTime() || d.getTime() === end.getTime()) {
+                maxHours = maxHours / 2;
+            }
+        }
 
         entries.push({
             date: dateStr,