test: assert events for the remaining action types

expand had no event assertion at all; build and mission-complete asserted
type/message but not the event's turn. Issue #11 requires every action type
to be covered with correct turn/type/message.

lib/game/missions.test.ts

@@ -185,6 +185,7 @@ describe('completion', () => {
     expect(reward.qty).toBe(2)
 
     const event = (await db.db.select().from(schema.events)).find((e) => e.type === 'mission' && /complete/i.test(e.message))!
+    expect(event.turn).toBe(4) // accept (1) + three scans (2–4); completion is written by the third scan
     expect(event.message).toContain('Scan 3 bodies')
   })