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/e2e/home-events.spec.ts

@@ -191,6 +191,133 @@ test.describe('FAB: Create Event Button', () => {
   })
 })
 
+test.describe('Temporal Grouping: Section Headers', () => {
+  test('events are distributed under correct section headers', async ({ page }) => {
+    // Use dates relative to "now" to ensure correct section assignment
+    const now = new Date()
+    const todayEvent: StoredEvent = {
+      eventToken: 'today-1',
+      title: 'Today Standup',
+      dateTime: new Date(now.getFullYear(), now.getMonth(), now.getDate(), 18, 0, 0).toISOString(),
+      expiryDate: '',
+    }
+    const laterEvent: StoredEvent = {
+      eventToken: 'later-1',
+      title: 'Future Conference',
+      dateTime: new Date(now.getFullYear() + 1, 0, 15, 10, 0, 0).toISOString(),
+      expiryDate: '',
+    }
+    await page.addInitScript(seedEvents([todayEvent, laterEvent, pastEvent]))
+    await page.goto('/')
+
+    // Verify section headers appear
+    await expect(page.getByRole('heading', { name: 'Today', level: 2 })).toBeVisible()
+    await expect(page.getByRole('heading', { name: 'Later', level: 2 })).toBeVisible()
+    await expect(page.getByRole('heading', { name: 'Past', level: 2 })).toBeVisible()
+
+    // Events are in the correct sections
+    const sections = page.locator('.event-section')
+    const todaySection = sections.filter({ has: page.getByRole('heading', { name: 'Today', level: 2 }) })
+    await expect(todaySection.getByText('Today Standup')).toBeVisible()
+
+    const laterSection = sections.filter({ has: page.getByRole('heading', { name: 'Later', level: 2 }) })
+    await expect(laterSection.getByText('Future Conference')).toBeVisible()
+
+    const pastSection = sections.filter({ has: page.getByRole('heading', { name: 'Past', level: 2 }) })
+    await expect(pastSection.getByText('New Year Party')).toBeVisible()
+  })
+
+  test('empty sections are not rendered', async ({ page }) => {
+    // Only a past event — no Today, This Week, or Later sections
+    await page.addInitScript(seedEvents([pastEvent]))
+    await page.goto('/')
+
+    await expect(page.getByRole('heading', { name: 'Past', level: 2 })).toBeVisible()
+    await expect(page.getByRole('heading', { name: 'Today', level: 2 })).toHaveCount(0)
+    await expect(page.getByRole('heading', { name: 'This Week', level: 2 })).toHaveCount(0)
+    await expect(page.getByRole('heading', { name: 'Next Week', level: 2 })).toHaveCount(0)
+    await expect(page.getByRole('heading', { name: 'Later', level: 2 })).toHaveCount(0)
+  })
+
+  test('Today section header has emphasis CSS class', async ({ page }) => {
+    const now = new Date()
+    const todayEvent: StoredEvent = {
+      eventToken: 'today-emph',
+      title: 'Emphasis Test',
+      dateTime: new Date(now.getFullYear(), now.getMonth(), now.getDate(), 20, 0, 0).toISOString(),
+      expiryDate: '',
+    }
+    await page.addInitScript(seedEvents([todayEvent]))
+    await page.goto('/')
+
+    const todayHeader = page.getByRole('heading', { name: 'Today', level: 2 })
+    await expect(todayHeader).toHaveClass(/section-header--emphasized/)
+  })
+})
+
+test.describe('Temporal Grouping: Date Subheaders', () => {
+  test('no date subheader in Today section', async ({ page }) => {
+    const now = new Date()
+    const todayEvent: StoredEvent = {
+      eventToken: 'today-sub',
+      title: 'No Subheader Test',
+      dateTime: new Date(now.getFullYear(), now.getMonth(), now.getDate(), 19, 0, 0).toISOString(),
+      expiryDate: '',
+    }
+    await page.addInitScript(seedEvents([todayEvent]))
+    await page.goto('/')
+
+    const todaySection = page.locator('.event-section').filter({
+      has: page.getByRole('heading', { name: 'Today', level: 2 }),
+    })
+    await expect(todaySection.locator('.date-subheader')).toHaveCount(0)
+  })
+
+  test('date subheaders appear in Later section', async ({ page }) => {
+    await page.addInitScript(seedEvents([futureEvent1, futureEvent2]))
+    await page.goto('/')
+
+    const laterSection = page.locator('.event-section').filter({
+      has: page.getByRole('heading', { name: 'Later', level: 2 }),
+    })
+    // Both future events are on different dates, so expect subheaders
+    const subheaders = laterSection.locator('.date-subheader')
+    await expect(subheaders).toHaveCount(2)
+  })
+
+  test('date subheaders appear in Past section', async ({ page }) => {
+    await page.addInitScript(seedEvents([pastEvent]))
+    await page.goto('/')
+
+    const pastSection = page.locator('.event-section').filter({
+      has: page.getByRole('heading', { name: 'Past', level: 2 }),
+    })
+    await expect(pastSection.locator('.date-subheader')).toHaveCount(1)
+  })
+})
+
+test.describe('Temporal Grouping: Time Display', () => {
+  test('future event cards show clock time', async ({ page }) => {
+    await page.addInitScript(seedEvents([futureEvent1]))
+    await page.goto('/')
+
+    const timeLabel = page.locator('.event-card__time')
+    const text = await timeLabel.first().textContent()
+    // Should show clock time (e.g., "18:00" or "6:00 PM"), not relative time
+    expect(text).toMatch(/\d{1,2}[:.]\d{2}/)
+  })
+
+  test('past event cards show relative time', async ({ page }) => {
+    await page.addInitScript(seedEvents([pastEvent]))
+    await page.goto('/')
+
+    const timeLabel = page.locator('.event-card__time')
+    const text = await timeLabel.first().textContent()
+    // Should show relative time like "X years ago" or "last year"
+    expect(text).toMatch(/ago|last|yesterday/)
+  })
+})
+
 test.describe('US1: View My Events', () => {
   test('displays all stored events with title and relative time', async ({ page }) => {
     await page.addInitScript(seedEvents([futureEvent1, futureEvent2, pastEvent]))