feat(day): single-column day view, wire into view switcher

Day view as a one-column slice of the week view: shared TimedBlock/
AllDaySpan layout, per-day swipe navigation, hoisted noon-centred scroll,
animated all-day strip, and a compact top bar showing the full date.

- DayUiState / DayViewModel / DayScreen under ui/day
- reuse layoutDay/layoutAllDay/coversDay from the week package
- add Day to IMPLEMENTED_VIEWS; CalendarHost routes it explicitly
- day_today_action strings (en/de)

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

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

@@ -7,6 +7,7 @@ import androidx.compose.runtime.saveable.rememberSaveable
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import de.jeanlucmakiola.calendula.ui.common.CalendarView
+import de.jeanlucmakiola.calendula.ui.day.DayScreen
 import de.jeanlucmakiola.calendula.ui.month.MonthScreen
 import de.jeanlucmakiola.calendula.ui.week.WeekScreen
 
@@ -26,8 +27,12 @@ fun CalendarHost(modifier: Modifier = Modifier) {
             onSelectView = onSelectView,
             modifier = modifier,
         )
-        // Month, plus Day as a fallback until the day view lands (v0.5).
-        else -> MonthScreen(
+        CalendarView.Day -> DayScreen(
+            selectedView = view,
+            onSelectView = onSelectView,
+            modifier = modifier,
+        )
+        CalendarView.Month -> MonthScreen(
             selectedView = view,
             onSelectView = onSelectView,
             modifier = modifier,