fix: add tsup --shims for ESM/CJS dirname compatibility (#308)

Bare __dirname is a CJS-only global and is undefined in ESM contexts.
Enable tsup --shims so both the ESM and CJS builds get proper polyfills
for __dirname, __filename, and import.meta.url respectively.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Niki2k1

packages/sync-engine/package.json

@@ -18,7 +18,7 @@
   "scripts": {
     "clean": "rimraf dist",
     "prebuild": "npm run clean",
-    "build": "tsup src/index.ts --format esm,cjs --dts && cp -r src/database/migrations dist/migrations",
+    "build": "tsup src/index.ts --format esm,cjs --dts --shims && cp -r src/database/migrations dist/migrations",
     "lint": "eslint src --ext .ts"
   },
   "files": [