feat(core): Change workflow deletions to soft deletes (#14894)

Adds soft‑deletion support for workflows through a new boolean column `isArchived`.

When a workflow is archived we now set `isArchived` flag to true and the workflows
stays in the database and is omitted from the default workflow listing query.

Archived workflows can be viewed in read-only mode, but they cannot be activated.

Archived workflows are still available by ID and can be invoked as sub-executions,
so existing Execute Workflow nodes continue to work. Execution engine doesn't
care about isArchived flag.

Users can restore workflows via Unarchive action at the UI.

packages/frontend/editor-ui/src/composables/useWorkflowSaving.ts

@@ -32,9 +32,8 @@ export function useWorkflowSaving({ router }: { router: ReturnType<typeof useRou
 			cancel?: () => Promise<void>;
 		} = {},
 	) {
-		if (!uiStore.stateIsDirty) {
+		if (!uiStore.stateIsDirty || workflowsStore.workflow.isArchived) {
 			next();
-
 			return;
 		}