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-core/src/lib.rs

@@ -0,0 +1,19 @@
+//! mailer-core: Email model, validation, and RFC 5322 primitives.
+
+/// Re-export mailparse for MIME parsing.
+pub use mailparse;
+
+/// Placeholder for email address validation and data types.
+pub fn version() -> &'static str {
+    env!("CARGO_PKG_VERSION")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_version() {
+        assert!(!version().is_empty());
+    }
+}