fix(malachite-web): fix $core alias and Vercel install path post-monorepo migration

packages/malachite-web/svelte.config.js

···
       // Shared, environment-agnostic core — single source of truth.
       // CLI uses src/core/ directly; web imports via this alias so there is
       // no duplicated logic.
-      $core: resolve(__dirname, '../src/core'),
+      $core: resolve(__dirname, '../malachite/src/core'),
     },
   },
 };

packages/malachite-web/vercel.json

···
 {
   "framework": "sveltekit",
   "buildCommand": "pnpm build",
-  "installCommand": "cd .. && pnpm install",
+  "installCommand": "cd ../.. && pnpm install",
   "outputDirectory": ".vercel/output"
 }