fix: timestamp in wrong timezone after save

index.html

@@ -215,7 +215,7 @@
 
   <div id="floating-menu" role="menu" aria-label="Navigation menu">
     <button id="nav-entries" role="menuitem">Trash</button>
-      <button id="nav-import" role="menuitem">Import</button>
+    <button id="nav-import" role="menuitem">Import</button>
     <button id="nav-export" role="menuitem">Export</button>
   </div>
 
@@ -230,6 +230,15 @@
   </div>
 
   <script>
+    function formatDateToLocalInput(date) {
+      const pad = (n) => n.toString().padStart(2, '0');
+      const year = date.getFullYear();
+      const month = pad(date.getMonth() + 1);
+      const day = pad(date.getDate());
+      const hours = pad(date.getHours());
+      const minutes = pad(date.getMinutes());
+      return `${year}-${month}-${day}T${hours}:${minutes}`;
+    }
     const STORAGE_KEY = 'milkProductionEntries';
     const REMOVED_KEY = 'milkProductionRemoved';
 
@@ -238,7 +247,7 @@
 
     const listEl = document.getElementById('list');
     const timestampInput = document.getElementById('timestamp');
-    timestampInput.value = new Date().toISOString().slice(0, 16);
+    timestampInput.value = formatDateToLocalInput(new Date());
     const amountInput = document.getElementById('amount');
     const submitBtn = document.getElementById('submit-btn');
 
@@ -404,7 +413,8 @@
       entries.push(newEntry);
       save();
       render();
-      timestampInput.value = new Date().toISOString().slice(0, 16);
+
+      timestampInput.value = formatDateToLocalInput(new Date());
       amountInput.value = '';
       updateSubmitState();
     });
@@ -491,7 +501,7 @@
     }
 
     function downloadJSONFile(filename = 'data.json') {
-      const blob = new Blob([JSON.stringify(entries)], { type: 'application/json' });
+      const blob = new Blob([JSON.stringify(entries)], {type: 'application/json'});
       const url = URL.createObjectURL(blob);
       const a = document.createElement('a');
       a.href = url;