feat(DateTimePicker): implement calendar open handler to preserve scroll position

feat(Modal): remove max height restriction for modal body
style: clean up z-index for datepicker popper

src/components/DateTimePicker.jsx

@@ -1,7 +1,7 @@
 import ReactDatePicker from 'react-datepicker';
 import { de } from 'date-fns/locale';
 import { Calendar as CalendarIcon, Clock } from 'lucide-react';
-import { forwardRef } from 'react';
+import { forwardRef, useRef, useCallback } from 'react';
 import 'react-datepicker/dist/react-datepicker.css';
 
 /**
@@ -39,8 +39,29 @@ export default function DateTimePicker({
 
   const Icon = icon === 'clock' ? Clock : CalendarIcon;
 
-  return (
-    <div className="dtp-wrapper">
+  // react-datepicker calls scrollIntoView on the selected time item when the
+  // calendar opens. This scrolls the nearest scrollable ancestor (page or
+  // modal). We capture every scrollable ancestor's position just before open
+  // and restore it in the next animation frame — after scrollIntoView fires.
+  const wrapperRef = useRef(null);
+  const handleCalendarOpen = useCallback(() => {
+    const snapshots = [];
+    let el = wrapperRef.current?.parentElement;
+    while (el && el !== document.body) {
+      const { overflow, overflowY } = getComputedStyle(el);
+      if (/(auto|scroll)/.test(overflow + overflowY)) {
+        snapshots.push({ el, top: el.scrollTop, left: el.scrollLeft });
+      }
+      el = el.parentElement;
+    }
+    // also capture window scroll
+    const winY = window.scrollY;
+    requestAnimationFrame(() => {
+      snapshots.forEach(s => { s.el.scrollTop = s.top; s.el.scrollLeft = s.left; });
+      window.scrollTo({ top: winY, behavior: 'instant' });
+    });
+  }, []);
+    <div className="dtp-wrapper" ref={wrapperRef}>
       {label && (
         <label className="block text-sm font-medium text-th-text mb-1.5">
           {label}{required && ' *'}
@@ -59,6 +80,7 @@ export default function DateTimePicker({
           minDate={minDate}
           required={required}
           popperPlacement="bottom-start"
+          onCalendarOpen={handleCalendarOpen}
           popperModifiers={[
             { name: 'offset', options: { offset: [0, 4] } },
             { name: 'preventOverflow', options: { rootBoundary: 'viewport', tether: false, altAxis: true } },

src/components/Modal.jsx

@@ -16,7 +16,7 @@ export default function Modal({ title, children, onClose, maxWidth = 'max-w-lg'
           </button>
         </div>
         {/* Body */}
-        <div className="p-6 overflow-y-auto max-h-[calc(90vh-4rem)]">
+        <div className="p-6">
           {children}
         </div>
       </div>

src/index.css

@@ -819,11 +819,6 @@
   display: none;
 }
 
-/* Must sit above the modal backdrop (z-50 stacking context) */
-.react-datepicker-popper {
-  z-index: 200 !important;
-}
-
 /* ── Header (custom rendered) ─────────────────────────────────── */
 .dtp-calendar .react-datepicker__header {
   background: var(--bg-secondary);