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

crates/domain/src/value_objects/user_id.rs

@@ -0,0 +1,22 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
+pub struct UserId(uuid::Uuid);
+
+impl UserId {
+    pub fn new() -> Self { Self(uuid::Uuid::new_v4()) }
+    pub fn from_uuid(id: uuid::Uuid) -> Self { Self(id) }
+    pub fn as_uuid(&self) -> &uuid::Uuid { &self.0 }
+}
+
+impl Default for UserId {
+    fn default() -> Self { Self::new() }
+}
+
+impl std::fmt::Display for UserId {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl From<uuid::Uuid> for UserId {
+    fn from(id: uuid::Uuid) -> Self { Self(id) }
+}