core: clarify postinstall error message when binary is missing

Users installing with pnpm or --ignore-scripts now see a clear explanation
of why the native binary is missing and exact steps to fix it. The shell
script wrapper provides more actionable guidance than the previous Node.js
fallback that only suggested running the postinstall script without context
about why it wasn't run automatically.

packages/opencode/script/publish.ts

@@ -37,9 +37,16 @@ await $`cp ./script/postinstall.mjs ./dist/${pkg.name}/postinstall.mjs`
 await Bun.file(`./dist/${pkg.name}/LICENSE`).write(await Bun.file("../../LICENSE").text())
 await Bun.file(`./dist/${pkg.name}/bin/${pkg.name}.exe`).write(
   [
-    "#!/usr/bin/env node",
-    "console.error('The opencode native binary was not installed. Run `node postinstall.mjs` from the opencode-ai package directory to finish setup.')",
-    "process.exit(1)",
+    `echo "Error: ${pkg.name}-ai's postinstall script was not run." >&2`,
+    'echo "" >&2',
+    'echo "This occurs when using --ignore-scripts during installation, or when using a" >&2',
+    'echo "package manager like pnpm that does not run postinstall scripts by default." >&2',
+    'echo "" >&2',
+    'echo "To fix this, run the postinstall script manually:" >&2',
+    `echo "  cd node_modules/${pkg.name}-ai && node postinstall.mjs" >&2`,
+    'echo "" >&2',
+    `echo "Or reinstall ${pkg.name}-ai without the --ignore-scripts flag." >&2`,
+    "exit 1",
     "",
   ].join("\n"),
 )