Add core build script

core/build.rs

@@ -0,0 +1,5 @@
+// build.rs for UniFFI codegen (optional, no-op if uniffi-bindgen not present)
+fn main() {
+    println!("cargo:rerun-if-changed=uniffi/cryptec.udl");
+    // Optionally, invoke uniffi-bindgen here for local dev builds
+}