feat(domain): value objects, entities, port traits with tests

crates/domain/src/value_objects/role.rs

@@ -0,0 +1,23 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+#[serde(rename_all = "lowercase")]
+pub enum Role { User, Admin }
+
+impl std::fmt::Display for Role {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Role::User => write!(f, "user"),
+            Role::Admin => write!(f, "admin"),
+        }
+    }
+}
+
+impl std::str::FromStr for Role {
+    type Err = String;
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s {
+            "user" => Ok(Role::User),
+            "admin" => Ok(Role::Admin),
+            other => Err(format!("Unknown role: {other}")),
+        }
+    }
+}