build: re-enable `prepare` script for husky setup

Re-enables the `pnpm run prepare` script.

The prepare script is automatically run when running
`pnpm install` locally.

It both:
  - Sets up husky/git pre-commit scripts
  - Builds the `packages/mermaid/dist` folder.

package.json

@@ -46,7 +46,7 @@
     "test": "pnpm lint && vitest run",
     "test:watch": "vitest --coverage --watch",
     "prepublishOnly": "pnpm build && pnpm test",
-    "todo-prepare": "concurrently \"husky install\" \"pnpm build\"",
+    "prepare": "concurrently \"husky install\" \"pnpm build\"",
     "pre-commit": "lint-staged"
   },
   "repository": {