feat: open Day view when tapping a date header in Week/Agenda

Tapping a date header in the Week (day-of-week column) and Agenda
(sticky section) views now drills into that date in Day view, mirroring
the Agenda widget's header behaviour. Both reuse the existing onOpenDay
callback (pendingDayIso + drillToDay) that Month already used, so the
back stack lands on Day with the tapped view as its parent.

Month already navigated on any cell tap (the transparent tap layer sits
above the day number), so no change was needed there — all four views
now behave consistently.

Closes #37

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/main/java/de/jeanlucmakiola/calendula/ui/CalendarHost.kt

@@ -284,6 +284,7 @@ fun CalendarHost(
                 CalendarView.Week -> WeekScreen(
                     selectedView = currentView,
                     onSelectView = onSelectView,
+                    onOpenDay = onOpenDay,
                     onEventClick = onEventClick,
                     onOpenSettings = onOpenSettings,
                     onOpenSearch = onOpenSearch,
@@ -315,6 +316,7 @@ fun CalendarHost(
                 CalendarView.Agenda -> AgendaScreen(
                     selectedView = currentView,
                     onSelectView = onSelectView,
+                    onOpenDay = onOpenDay,
                     onEventClick = onEventClick,
                     onOpenSettings = onOpenSettings,
                     onOpenSearch = onOpenSearch,

app/src/main/java/de/jeanlucmakiola/calendula/ui/agenda/AgendaScreen.kt

@@ -93,6 +93,7 @@ private val zone = TimeZone.currentSystemDefault()
 fun AgendaScreen(
     selectedView: CalendarView,
     onSelectView: (CalendarView) -> Unit,
+    onOpenDay: (LocalDate) -> Unit,
     onEventClick: (EventInstance) -> Unit,
     onOpenSettings: () -> Unit,
     onOpenSearch: () -> Unit,
@@ -191,6 +192,7 @@ fun AgendaScreen(
                     pastDisplay = pastDisplay,
                     onRetry = viewModel::goToToday,
                     onEventClick = onEventClick,
+                    onOpenDay = onOpenDay,
                     modifier = Modifier
                         .weight(1f)
                         .fillMaxWidth(),
@@ -289,6 +291,7 @@ private fun AgendaContent(
     pastDisplay: PastEventDisplay,
     onRetry: () -> Unit,
     onEventClick: (EventInstance) -> Unit,
+    onOpenDay: (LocalDate) -> Unit,
     modifier: Modifier = Modifier,
 ) {
     when (state) {
@@ -318,6 +321,7 @@ private fun AgendaContent(
                     dimPast = pastDisplay == PastEventDisplay.DIM,
                     now = now,
                     onEventClick = onEventClick,
+                    onOpenDay = onOpenDay,
                     modifier = modifier,
                 )
             }
@@ -333,6 +337,7 @@ private fun AgendaList(
     dimPast: Boolean,
     now: Instant,
     onEventClick: (EventInstance) -> Unit,
+    onOpenDay: (LocalDate) -> Unit,
     modifier: Modifier = Modifier,
 ) {
     LazyColumn(
@@ -342,7 +347,7 @@ private fun AgendaList(
     ) {
         days.forEach { day ->
             stickyHeader(key = "header-${day.date}") {
-                AgendaDayHeader(date = day.date, today = today)
+                AgendaDayHeader(date = day.date, today = today, onOpenDay = onOpenDay)
             }
             itemsIndexed(
                 items = day.events,
@@ -362,10 +367,16 @@ private fun AgendaList(
 }
 
 @Composable
-private fun AgendaDayHeader(date: LocalDate, today: LocalDate) {
+private fun AgendaDayHeader(
+    date: LocalDate,
+    today: LocalDate,
+    onOpenDay: (LocalDate) -> Unit,
+) {
     Surface(
         color = MaterialTheme.colorScheme.surface,
-        modifier = Modifier.fillMaxWidth(),
+        modifier = Modifier
+            .fillMaxWidth()
+            .clickable { onOpenDay(date) },
     ) {
         Text(
             text = agendaDayLabel(date, today),

app/src/main/java/de/jeanlucmakiola/calendula/ui/week/WeekScreen.kt

@@ -128,6 +128,7 @@ private fun WeekUiState.Success.allDayStripHeight(): Dp {
 fun WeekScreen(
     selectedView: CalendarView,
     onSelectView: (CalendarView) -> Unit,
+    onOpenDay: (LocalDate) -> Unit,
     onEventClick: (EventInstance) -> Unit,
     onOpenSettings: () -> Unit,
     onOpenSearch: () -> Unit,
@@ -249,6 +250,7 @@ fun WeekScreen(
                     onSwipePrev = goPrev,
                     onRetry = jumpToToday,
                     onEventClick = onEventClick,
+                    onOpenDay = onOpenDay,
                     onCreateAt = { d, minutes -> onCreateEvent(d, minutes) },
                     modifier = Modifier
                         .padding(innerPadding)
@@ -268,6 +270,7 @@ private fun WeekContent(
     onSwipePrev: () -> Unit,
     onRetry: () -> Unit,
     onEventClick: (EventInstance) -> Unit,
+    onOpenDay: (LocalDate) -> Unit,
     onCreateAt: (LocalDate, Int) -> Unit,
     modifier: Modifier = Modifier,
 ) {
@@ -342,6 +345,7 @@ private fun WeekContent(
                 scrollState = scrollState,
                 allDayHeight = allDayHeight,
                 onEventClick = onEventClick,
+                onOpenDay = onOpenDay,
                 onCreateAt = onCreateAt,
             )
         }
@@ -355,6 +359,7 @@ private fun WeekSuccess(
     scrollState: ScrollState,
     allDayHeight: Dp,
     onEventClick: (EventInstance) -> Unit,
+    onOpenDay: (LocalDate) -> Unit,
     onCreateAt: (LocalDate, Int) -> Unit,
 ) {
     Column(modifier = Modifier.fillMaxSize()) {
@@ -363,7 +368,7 @@ private fun WeekSuccess(
                 .fillMaxWidth()
                 .background(topSectionColor),
         ) {
-            WeekDayHeader(days = state.days, today = state.today)
+            WeekDayHeader(days = state.days, today = state.today, onOpenDay = onOpenDay)
             AllDayStrip(state = state, height = allDayHeight, onEventClick = onEventClick)
         }
         // Breathing room between the (colour-shifting) top section and the
@@ -427,7 +432,11 @@ private fun WeekTopBar(
 }
 
 @Composable
-private fun WeekDayHeader(days: List<LocalDate>, today: LocalDate) {
+private fun WeekDayHeader(
+    days: List<LocalDate>,
+    today: LocalDate,
+    onOpenDay: (LocalDate) -> Unit,
+) {
     val locale = currentLocale()
     val weekStart = days.first()
     val weekNumber = remember(weekStart) {
@@ -453,7 +462,10 @@ private fun WeekDayHeader(days: List<LocalDate>, today: LocalDate) {
             val javaDow = java.time.DayOfWeek.of(date.dayOfWeek.ordinal + 1)
             val isToday = date == today
             Column(
-                modifier = Modifier.weight(1f),
+                modifier = Modifier
+                    .weight(1f)
+                    .clip(RoundedCornerShape(12.dp))
+                    .clickable { onOpenDay(date) },
                 horizontalAlignment = Alignment.CenterHorizontally,
             ) {
                 Text(