Add readiness probe endpoint with DB connectivity check

src/api/health.rs

@@ -4,3 +4,12 @@ use serde_json::{json, Value};
 pub async fn health_check() -> (StatusCode, Json<Value>) {
     (StatusCode::OK, Json(json!({ "status": "ok", "version": env!("CARGO_PKG_VERSION") })))
 }
+
+pub async fn readiness_check(
+    axum::extract::State(pool): axum::extract::State<sqlx::PgPool>,
+) -> axum::http::StatusCode {
+    match sqlx::query("SELECT 1").fetch_one(&pool).await {
+        Ok(_) => axum::http::StatusCode::OK,
+        Err(_) => axum::http::StatusCode::SERVICE_UNAVAILABLE,
+    }
+}