chore add core rust project files and diesel migrations

Track required workspace crates, scripts, and historical diesel migrations so the repository contains the complete runnable backend baseline.

Made-with: Cursor

htyts_models/src/req_cron.rs

@@ -0,0 +1,8 @@
+use serde::{Deserialize, Serialize};
+
+/// Java `ReqCron` (`expr` optional).
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
+pub struct ReqCron {
+    #[serde(default)]
+    pub expr: Option<String>,
+}