Snap Beginn/Ende to next 15-minute boundary on change and on load

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/LogbuchForm.tsx

@@ -19,10 +19,24 @@ function toLocalDatetimeValue(isoOrDatetime: string): string {
   return isoOrDatetime.slice(0, 16);
 }
 
+function snapTo15(value: string): string {
+  if (!value) return value;
+  const d = new Date(value);
+  if (isNaN(d.getTime())) return value;
+  const rem = d.getMinutes() % 15;
+  if (rem !== 0) {
+    d.setMinutes(d.getMinutes() + (15 - rem));
+    d.setSeconds(0);
+  }
+  const pad = (n: number) => String(n).padStart(2, '0');
+  return `${d.getFullYear()}-${pad(d.getMonth() + 1)}-${pad(d.getDate())}T${pad(d.getHours())}:${pad(d.getMinutes())}`;
+}
+
 function nowLocalDatetime(): string {
   const now = new Date();
   const pad = (n: number) => String(n).padStart(2, '0');
-  return `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}T${pad(now.getHours())}:${pad(now.getMinutes())}`;
+  const raw = `${now.getFullYear()}-${pad(now.getMonth() + 1)}-${pad(now.getDate())}T${pad(now.getHours())}:${pad(now.getMinutes())}`;
+  return snapTo15(raw);
 }
 
 const NO_OBJEKTE_ARTEN: ArtFuehrung[] = ['BEO-Sitzung', 'Technischer Dienst'];
@@ -160,7 +174,7 @@ export default function LogbuchForm({ kuppel, currentUserBeo, editEntry, onSaved
   const labelCls = 'block text-sm font-medium text-gray-700 mb-0.5';
 
   return (
-    <form onSubmit={handleSubmit} className="space-y-3 max-w-2xl">
+    <form onSubmit={handleSubmit} className="space-y-3 max-w-2xl mx-auto border-2 border-gray-400 rounded-xl p-4 bg-white">
 
       {/* Art der Führung — volle Breite */}
       <div>
@@ -179,8 +193,9 @@ export default function LogbuchForm({ kuppel, currentUserBeo, editEntry, onSaved
           <input
             type="datetime-local"
             value={beginn}
-            onChange={(e) => setBeginn(e.target.value)}
+            onChange={(e) => setBeginn(snapTo15(e.target.value))}
             required
+            step={900}
             className="w-full px-2 py-2 border-2 border-gray-400 rounded-lg bg-white text-sm focus:border-blue-500 focus:outline-none"
           />
         </div>
@@ -189,8 +204,9 @@ export default function LogbuchForm({ kuppel, currentUserBeo, editEntry, onSaved
           <input
             type="datetime-local"
             value={ende}
-            onChange={(e) => setEnde(e.target.value)}
+            onChange={(e) => setEnde(snapTo15(e.target.value))}
             required
+            step={900}
             className="w-full px-2 py-2 border-2 border-gray-400 rounded-lg bg-white text-sm focus:border-blue-500 focus:outline-none"
           />
         </div>
@@ -270,8 +286,8 @@ export default function LogbuchForm({ kuppel, currentUserBeo, editEntry, onSaved
         </div>
       )}
 
-      {/* Buttons — volle Breite auf Mobile */}
+      {/* Buttons — zentriert */}
-      <div className="flex flex-col sm:flex-row gap-3">
+      <div className="flex flex-col sm:flex-row gap-3 justify-center">
         <button
           type="submit"
           disabled={saving}