docs: mark multi-value (List) attribute feature complete; document DataType.List + ElementDataType in Component-Commons

MV-15 integration checkpoint: full solution builds 0/0; feature-targeted tests
green across Commons, TemplateEngine, SiteRuntime, DataConnectionLayer,
Communication, Transport, ManagementService, CLI, CentralUI (255 tests).

docs/requirements/Component-Commons.md

@@ -26,7 +26,7 @@ Referenced by all component libraries and the Host.
 
 Commons must define shared primitive and utility types used across multiple components, including but not limited to:
 
-- **`DataType` enum**: Enumerates the data types supported by the system (e.g., Boolean, Int32, Float, Double, String, DateTime, Binary).
+- **`DataType` enum**: Enumerates the data types supported by the system: Boolean, Int32, Float, Double, String, DateTime, Binary, and **List** (a homogeneous multi-value attribute). A `List` attribute carries a companion `ElementDataType` (one of the scalar types — String, Int32, Float, Double, Boolean, DateTime; not Binary, not nested List) on `TemplateAttribute` / `InstanceAttributeOverride` and the flattened `ResolvedAttribute`. List values are stored and transmitted as a canonical JSON array via the `AttributeValueCodec` helper (scalars keep their historical invariant-culture string form); the `ElementDataType` is fixed by the defining level and cannot be changed on a derived template or instance override.
 - **`RetryPolicy`**: A record or immutable class describing retry behavior (max retries, fixed delay between retries).
 - **`Result<T>`**: A discriminated result type that represents either a success value or an error, enabling consistent error handling across component boundaries without exceptions.
 - **`InstanceState` enum**: Enabled, Disabled.