refactor(mystery): remove story.ts; endings live in markdown

src/world/story.ts

@@ -1,17 +0,0 @@
-import type { World } from './types'
-
-export const endings: World['endings'] = {
-  true: {
-    whenFlags: { ratGone: true },
-    narration:
-      'You stand at the top of the stair. The thing below has settled. The door behind you opens, and outside, finally, is morning.',
-  },
-  wrong: {
-    whenFlags: {},
-    narration: '',  // unreachable in sample world
-  },
-  bad: {
-    whenFlags: {},
-    narration: '',  // unreachable in sample world
-  },
-}