api: GET /api/system + POST /api/explore, OpenAPI spec updated in code

app/api/system/route.ts

@@ -0,0 +1,8 @@
+import { getGameDb } from '@/lib/db/client'
+import { getSystemState } from '@/lib/game/save'
+
+// The current system's bodies (planets + moons) and the save's inventory; auto-initializes on first hit.
+export async function GET() {
+  const db = await getGameDb()
+  return Response.json(await getSystemState(db))
+}