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

rust/crates/mailer-bin/src/main.rs

@@ -0,0 +1,11 @@
+//! mailer-bin: Standalone Rust binary for the @serve.zone/mailer network stack.
+
+fn main() {
+    println!(
+        "mailer-bin v{} (core: {}, smtp: {}, security: {})",
+        env!("CARGO_PKG_VERSION"),
+        mailer_core::version(),
+        mailer_smtp::version(),
+        mailer_security::version(),
+    );
+}