Add temporal grouping to event list (Today/This Week/Next Week/Later/Past)

Group events into five temporal sections with section headers, date subheaders,
and context-aware time display (clock time for upcoming, relative for past).
Includes new useEventGrouping composable, SectionHeader and DateSubheader
components, full unit and E2E test coverage.

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

frontend/src/composables/useEventGrouping.ts

@@ -0,0 +1,149 @@
+import type { StoredEvent } from './useEventStorage'
+
+export type SectionKey = 'today' | 'thisWeek' | 'nextWeek' | 'later' | 'past'
+
+export interface DateGroup {
+  dateKey: string
+  label: string
+  events: StoredEvent[]
+  showSubheader: boolean
+}
+
+export interface EventSection {
+  key: SectionKey
+  label: string
+  dateGroups: DateGroup[]
+  emphasized: boolean
+}
+
+const SECTION_ORDER: SectionKey[] = ['today', 'thisWeek', 'nextWeek', 'later', 'past']
+
+const SECTION_LABELS: Record<SectionKey, string> = {
+  today: 'Today',
+  thisWeek: 'This Week',
+  nextWeek: 'Next Week',
+  later: 'Later',
+  past: 'Past',
+}
+
+function startOfDay(date: Date): Date {
+  const d = new Date(date)
+  d.setHours(0, 0, 0, 0)
+  return d
+}
+
+function endOfDay(date: Date): Date {
+  const d = new Date(date)
+  d.setHours(23, 59, 59, 999)
+  return d
+}
+
+function endOfWeek(date: Date): Date {
+  const d = new Date(date)
+  const dayOfWeek = d.getDay() // 0=Sun, 1=Mon, ..., 6=Sat
+  // ISO week: Monday is first day. End of week = Sunday.
+  // If today is Sunday (0), end of week is today.
+  // Otherwise, days until Sunday = 7 - dayOfWeek
+  const daysUntilSunday = dayOfWeek === 0 ? 0 : 7 - dayOfWeek
+  d.setDate(d.getDate() + daysUntilSunday)
+  return endOfDay(d)
+}
+
+function endOfNextWeek(date: Date): Date {
+  const thisWeekEnd = endOfWeek(date)
+  const d = new Date(thisWeekEnd)
+  d.setDate(d.getDate() + 7)
+  return endOfDay(d)
+}
+
+function toDateKey(date: Date): string {
+  const y = date.getFullYear()
+  const m = String(date.getMonth() + 1).padStart(2, '0')
+  const d = String(date.getDate()).padStart(2, '0')
+  return `${y}-${m}-${d}`
+}
+
+function formatDateLabel(date: Date): string {
+  return new Intl.DateTimeFormat(undefined, {
+    weekday: 'short',
+    day: 'numeric',
+    month: 'short',
+  }).format(date)
+}
+
+function classifyEvent(eventDate: Date, todayStart: Date, todayEnd: Date, weekEnd: Date, nextWeekEnd: Date): SectionKey {
+  if (eventDate < todayStart) return 'past'
+  if (eventDate <= todayEnd) return 'today'
+  if (eventDate <= weekEnd) return 'thisWeek'
+  if (eventDate <= nextWeekEnd) return 'nextWeek'
+  return 'later'
+}
+
+export function useEventGrouping(events: StoredEvent[], now: Date = new Date()): EventSection[] {
+  const todayStart = startOfDay(now)
+  const todayEnd = endOfDay(now)
+  const weekEnd = endOfWeek(now)
+  const nextWeekEnd = endOfNextWeek(now)
+
+  // Classify events into sections
+  const buckets: Record<SectionKey, StoredEvent[]> = {
+    today: [],
+    thisWeek: [],
+    nextWeek: [],
+    later: [],
+    past: [],
+  }
+
+  for (const event of events) {
+    const eventDate = new Date(event.dateTime)
+    const section = classifyEvent(eventDate, todayStart, todayEnd, weekEnd, nextWeekEnd)
+    buckets[section].push(event)
+  }
+
+  // Build sections
+  const sections: EventSection[] = []
+
+  for (const key of SECTION_ORDER) {
+    const sectionEvents = buckets[key]
+    if (sectionEvents.length === 0) continue
+
+    // Sort events
+    const ascending = key !== 'past'
+    sectionEvents.sort((a, b) => {
+      const diff = new Date(a.dateTime).getTime() - new Date(b.dateTime).getTime()
+      return ascending ? diff : -diff
+    })
+
+    // Group by date
+    const dateGroupMap = new Map<string, StoredEvent[]>()
+    for (const event of sectionEvents) {
+      const dateKey = toDateKey(new Date(event.dateTime))
+      const group = dateGroupMap.get(dateKey)
+      if (group) {
+        group.push(event)
+      } else {
+        dateGroupMap.set(dateKey, [event])
+      }
+    }
+
+    // Convert to DateGroup array (order preserved from sorted events)
+    const dateGroups: DateGroup[] = []
+    for (const [dateKey, groupEvents] of dateGroupMap) {
+      dateGroups.push({
+        dateKey,
+        label: formatDateLabel(new Date(groupEvents[0]!.dateTime)),
+        events: groupEvents,
+        showSubheader: key !== 'today',
+      })
+    }
+
+    sections.push({
+      key,
+      label: SECTION_LABELS[key],
+      dateGroups,
+      emphasized: key === 'today',
+    })
+  }
+
+  return sections
+}