Clarify that failed status refers to lifecycle

Author: LucaButBoring

docs/specification/draft/basic/utilities/tasks.mdx

@@ -622,7 +622,7 @@ Tasks can be in one of the following states:
 - `submitted`: The request has been received and queued for execution
 - `working`: The request is currently being processed
 - `completed`: The request completed successfully and results are available
-- `failed`: The request encountered an error during execution
+- `failed`: The task lifecycle itself encountered an error
 - `cancelled`: The request was cancelled before completion
 - `unknown`: A terminal fallback state for unexpected error conditions when the receiver cannot determine the actual task state