fix: center selected date pill in home screen date strip

On first open the ListView started at offset 0 (future end), leaving
today's pill out of view. Also, navigation always scrolled the pill to
the left edge instead of centering it.

Added _centeredOffset() helper and a post-frame jumpTo in initState()
so the initially selected date is centered immediately. Updated
_jumpToToday() and didUpdateWidget() to use the same centering formula.

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

client/lib/features/home/home_screen.dart

@@ -221,6 +221,14 @@ class _DateSelectorState extends State<_DateSelector> {
 
   double _offsetForIndex(int index) => index * (_pillWidth + _pillSpacing);
 
+  double _centeredOffset(int index) {
+    final rawOffset = _offsetForIndex(index);
+    if (!_scrollController.hasClients) return rawOffset;
+    final viewportWidth = _scrollController.position.viewportDimension;
+    final centeredOffset = rawOffset - viewportWidth / 2 + _pillWidth / 2;
+    return centeredOffset < 0 ? 0 : centeredOffset;
+  }
+
   void _selectPreviousDay() {
     final previousDay = widget.selectedDate.subtract(const Duration(days: 1));
     final previousDayNormalized =
@@ -250,7 +258,7 @@ class _DateSelectorState extends State<_DateSelector> {
     widget.onDateSelected(DateTime(today.year, today.month, today.day));
     if (_scrollController.hasClients) {
       _scrollController.animateTo(
-        _offsetForIndex(_futureDays),
+        _centeredOffset(_futureDays),
         duration: const Duration(milliseconds: 300),
         curve: Curves.easeInOut,
       );
@@ -261,6 +269,11 @@ class _DateSelectorState extends State<_DateSelector> {
   void initState() {
     super.initState();
     _scrollController = ScrollController();
+    WidgetsBinding.instance.addPostFrameCallback((_) {
+      if (!mounted) return;
+      final initialIndex = _indexForDate(widget.selectedDate);
+      _scrollController.jumpTo(_centeredOffset(initialIndex));
+    });
   }
 
   @override
@@ -270,7 +283,7 @@ class _DateSelectorState extends State<_DateSelector> {
     final newIndex = _indexForDate(widget.selectedDate);
     if (oldIndex != newIndex && _scrollController.hasClients) {
       _scrollController.animateTo(
-        _offsetForIndex(newIndex),
+        _centeredOffset(newIndex),
         duration: const Duration(milliseconds: 300),
         curve: Curves.easeInOut,
       );