fix(deps): install xlsx from @e965/xlsx npm mirror

The dependency was pinned to a direct tarball on cdn.sheetjs.com, which
now returns 403 (Cloudflare bot-challenge) to automated clients, breaking
bun install in CI. npm's own xlsx is frozen at 0.18.5, so switch to the
@e965/xlsx mirror which republishes the identical 0.20.3 CDN build to the
npm registry. No code changes needed — all imports use bare 'xlsx'.

Author: TheodoreSpeaks

apps/sim/package.json

@@ -212,7 +212,7 @@
     "twilio": "5.9.0",
     "undici": "7.28.0",
     "unpdf": "1.4.0",
-    "xlsx": "https://cdn.sheetjs.com/xlsx-0.20.3/xlsx-0.20.3.tgz",
+    "xlsx": "npm:@e965/xlsx@0.20.3",
     "zod": "4.3.6",
     "zustand": "^5.0.13"
   },