fix: update workflows for crossplatform bins (#2)

package.json

@@ -4,7 +4,7 @@
   "description": "Letta Code is a CLI tool for interacting with stateful Letta agents from the terminal.",
   "type": "module",
   "bin": {
-    "letta": "bin/letta"
+    "letta": "bin/letta.js"
   },
   "files": [
     "LICENSE",
@@ -42,7 +42,7 @@
     "fix": "bunx --bun @biomejs/biome@2.2.5 check --write src",
     "dev:ui": "bun --loader:.md=text --loader:.mdx=text --loader:.txt=text run src/index.ts",
     "build": "bun build src/index.ts --compile --loader:.md=text --loader:.mdx=text --loader:.txt=text --outfile bin/letta",
-    "prepublishOnly": "bun run build",
+    "prepublishOnly": "echo 'Binaries should be built in CI. Run bun run build for local development.'",
     "postinstall": "bun scripts/postinstall-patches.js || true"
   },
   "lint-staged": {