fix: image upload (add extension field) + ingredient groups

- Fix Mealie image upload 422: send required `extension` field in form data
- Parse ingredient groups from mindmegette (multiple div.ingredients
  containers with strong.ingredients-group titles)
- Show group headers in UI with dashed-border accent input
- Pass group markers through to Mealie as title-only ingredient entries

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

app/mealie.py

@@ -147,7 +147,17 @@ class MealieClient:
         ingredients = []
         for item in recipe.get("ingredients", []):
             if isinstance(item, dict):
-                ingredients.append(self._build_ingredient(item))
+                # Group header marker
+                if "group" in item and "food" not in item:
+                    ingredients.append({
+                        "referenceId": str(uuid.uuid4()),
+                        "title": item["group"],
+                        "note": "",
+                        "isFood": False,
+                        "disableAmount": True,
+                    })
+                else:
+                    ingredients.append(self._build_ingredient(item))
             else:
                 # Legacy: plain string
                 ingredients.append({
@@ -235,6 +245,7 @@ class MealieClient:
         r = self.session.put(
             f"{self.api_url}/api/recipes/{slug}/image",
             files=files,
+            data={"extension": ext},
             timeout=30,
         )
         r.raise_for_status()