feat(recipes): opt-in workflow embedding for widget recipe saves

Add a "Save Recipe with Workflow" action next to "Save Recipe" in the LoRA
widget context menu. It posts the current UI-format graph alongside the save
request so the stored preview embeds it and the recipe can send the graph back
to ComfyUI. Embedding stays opt-in rather than folded into "Save Recipe": the
workflow is by far the largest metadata field and its widget values may carry
sensitive data.

- web/comfyui: new menu entry; saveRecipeDirectly({ embedWorkflow }) posts the
  UI graph and reports the outcome (embedded / skipped) via toasts.
- save_recipe_from_widget handler: reads an optional JSON workflow field so the
  long-standing body-less POST keeps working, including from cached clients.
- RecipePersistenceService.save_recipe_from_widget: embeds the graph through
  the existing optimize_image workflow path, derives has_workflow by detection,
  and skips graphs above MAX_WORKFLOW_EMBED_BYTES with workflow_skipped.

py/utils/constants.py

@@ -41,6 +41,14 @@ PREVIEW_EXTENSIONS = [
 # Card preview image width
 CARD_PREVIEW_WIDTH = 480
 
+# Upper bound for a ComfyUI workflow embedded into a recipe preview on the
+# opt-in widget save path. The workflow is by far the largest metadata field
+# (tens of KB for a simple graph), so an anomalous graph — e.g. one carrying
+# base64 blobs in widget values — is skipped instead of inflating the preview.
+# Imports are deliberately not capped: their workflow comes from an image the
+# user already chose, and preserving it is the point.
+MAX_WORKFLOW_EMBED_BYTES = 256 * 1024
+
 # Width for optimized example images
 EXAMPLE_IMAGE_WIDTH = 832