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

crates/domain/src/value_objects/password.rs

@@ -0,0 +1,14 @@
+// Manual Debug — redacts hash to prevent it appearing in logs
+#[derive(Clone, serde::Serialize, serde::Deserialize)]
+pub struct PasswordHash(String);
+
+impl std::fmt::Debug for PasswordHash {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_tuple("PasswordHash").field(&"[redacted]").finish()
+    }
+}
+
+impl PasswordHash {
+    pub fn from_hash(hash: String) -> Self { Self(hash) }
+    pub fn as_str(&self) -> &str { &self.0 }
+}