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-napi/Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "mailer-napi"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+
+[lib]
+crate-type = ["cdylib"]
+
+[dependencies]
+mailer-core = { path = "../mailer-core" }
+mailer-smtp = { path = "../mailer-smtp" }
+mailer-security = { path = "../mailer-security" }
+napi.workspace = true
+napi-derive.workspace = true
+tokio.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+
+[build-dependencies]
+napi-build = "2"

rust/crates/mailer-napi/build.rs

@@ -0,0 +1,5 @@
+extern crate napi_build;
+
+fn main() {
+    napi_build::setup();
+}

rust/crates/mailer-napi/src/lib.rs

@@ -0,0 +1,15 @@
+//! mailer-napi: N-API bindings exposing Rust mailer to Node.js/TypeScript.
+
+use napi_derive::napi;
+
+/// Returns the version of the native mailer module.
+#[napi]
+pub fn get_version() -> String {
+    format!(
+        "mailer-napi v{} (core: {}, smtp: {}, security: {})",
+        env!("CARGO_PKG_VERSION"),
+        mailer_core::version(),
+        mailer_smtp::version(),
+        mailer_security::version(),
+    )
+}