Only send what is new, and lead with a picture

The window now starts at the last dispatch, so pressing send twice does not
repeat a digest. Cards prefer entries that have a cover, the newest one of
them opens the message as a full width image, and the page says when the
last digest went out.

tests/lib/weekly-report.test.ts

@@ -133,3 +133,25 @@ describe('Karten', () => {
 		expect(sections).toHaveLength(5)
 	})
 })
+
+describe('windowFor mit letztem Versand', () => {
+	it('beginnt beim letzten Versand, wenn der jünger ist', () => {
+		const { from } = windowFor(
+			new Date('2026-08-03T06:00:00.000Z'),
+			7,
+			new Date('2026-08-01T09:00:00.000Z'),
+		)
+
+		expect(from.toISOString()).toBe('2026-08-01T09:00:00.000Z')
+	})
+
+	it('bleibt bei sieben Tagen, wenn der letzte Versand älter ist', () => {
+		const { from } = windowFor(
+			new Date('2026-08-03T06:00:00.000Z'),
+			7,
+			new Date('2026-06-01T09:00:00.000Z'),
+		)
+
+		expect(from.toISOString()).toBe('2026-07-27T06:00:00.000Z')
+	})
+})