Number entries on publish, delete media, read the cover

- drafts stay unnumbered, the number is handed out when an entry goes live
- DELETE /api/v1/media/:id and a delete control in the media library
- cover_media_id in the draft read, coverMediaId and coverUrl in the archive read

tests/scripts/seed.test.ts

@@ -25,7 +25,7 @@ describe('seed', () => {
 			expect.arrayContaining(['trakk', 'mta360', 'mta-telematik', 'orbit', 'pulsar']),
 		)
 		expect(postRows.length).toBeGreaterThanOrEqual(6)
-		expect(postRows.every(post => post.number > 0)).toBe(true)
+		expect(postRows.every(post => post.status !== 'published' || (post.number ?? 0) > 0)).toBe(true)
 	})
 
 	it('ist zweimal hintereinander ausführbar', async () => {