feat(rust): scaffold Rust workspace and fix TypeScript build errors

- Add @git.zone/tsrust with linux_amd64/linux_arm64 cross-compilation
- Scaffold Rust workspace with 5 crates: mailer-core, mailer-smtp, mailer-security, mailer-napi, mailer-bin
- Fix all TypeScript compilation errors for upgraded dependencies (smartfile v13, mailauth v4.13, smartproxy v23)
- Replace smartfile.fs/memory with @push.rocks/smartfs throughout codebase
- Fix .ts import extensions to .js for NodeNext module resolution
- Update DKIMSignOptions usage to match mailauth v4.13 API
- Add MTA error classes with permissive signatures for legacy SMTP client
- Replace removed DcRouter/StorageManager/deliverability imports with local interfaces

npmextra.json

@@ -1 +1,5 @@
-{}
+{
+  "@git.zone/tsrust": {
+    "targets": ["linux_amd64", "linux_arm64"]
+  }
+}