fix: workflow blueprints freely editable after creation (preserve_user_graph)

canonicalize_workflow_config was silently rebuilding any workflow with
ui.blueprint or ui.preset == still_graph from the canonical template on
every save, preflight, and read — making blueprint-based workflows
effectively read-only.

Add preserve_user_graph=True flag that skips the rebuild blocks. Only
create_workflow still uses preserve_user_graph=False so blueprints are
correctly expanded at creation time.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/app/domains/rendering/workflow_router.py

@@ -264,7 +264,7 @@ async def _build_rollout_summary(
 
 
 async def _workflow_to_out(db: AsyncSession, wf: WorkflowDefinition) -> WorkflowDefinitionOut:
-    canonical_config = canonicalize_workflow_config(wf.config)
+    canonical_config = canonicalize_workflow_config(wf.config, preserve_user_graph=True)
     workflow_family = infer_workflow_family_from_config(canonical_config)
     supported_artifact_kinds = tuple(
         derive_supported_artifact_kinds_from_workflow_config(canonical_config)
@@ -408,7 +408,7 @@ def _build_workflow_preflight_for_config(
         submit_prepared_workflow_tasks,
     )
 
-    normalized_config = canonicalize_workflow_config(workflow_config)
+    normalized_config = canonicalize_workflow_config(workflow_config, preserve_user_graph=True)
     try:
         workflow_context = prepare_workflow_context(
             normalized_config,
@@ -942,7 +942,7 @@ async def update_workflow(
         wf.name = body.name
     if body.config is not None:
         try:
-            normalized_config = canonicalize_workflow_config(body.config)
+            normalized_config = canonicalize_workflow_config(body.config, preserve_user_graph=True)
             WorkflowConfig.model_validate(normalized_config)
         except (ValidationError, ValueError) as exc:
             detail = exc.errors() if isinstance(exc, ValidationError) else str(exc)
@@ -1033,7 +1033,7 @@ async def _dispatch_workflow_for_config(
     )
 
     try:
-        normalized_config = canonicalize_workflow_config(workflow_config)
+        normalized_config = canonicalize_workflow_config(workflow_config, preserve_user_graph=True)
         workflow_context = prepare_workflow_context(
             normalized_config,
             context_id=context_id,