feat: enhance group duty pin command functionality

- Updated the `pin_duty_cmd` to handle cases where no message ID is found by sending a new duty message, pinning it, saving the pin, and scheduling the next update.
- Improved error handling for message sending and pinning operations, providing appropriate replies based on success or failure.
- Enhanced unit tests to cover the new behavior, ensuring proper functionality and error handling in various scenarios.

webapp/js/hints.js

@@ -115,7 +115,14 @@ function buildDutyItemTimePrefix(item, idx, total, hintDay, sep, fromLabel, toLa
       if (endSameDay && endHHMM && endHHMM !== startHHMM) {
         timePrefix += " " + toLabel + sep + endHHMM;
       }
+    } else if (startSameDay && startHHMM) {
+      /* First of multiple, but starts today — show full range */
+      timePrefix = fromLabel + sep + startHHMM;
+      if (endSameDay && endHHMM && endHHMM !== startHHMM) {
+        timePrefix += " " + toLabel + sep + endHHMM;
+      }
     } else if (endHHMM) {
+      /* Continuation from previous day — only end time */
       timePrefix = toLabel + sep + endHHMM;
     }
   } else if (idx > 0) {