feat(recipes): add image upload, fix save 500, seed HelloFresh data

- Store hero image as base64 data URI in text column (V023 migration)
- Add file upload UI to RecipeForm with FileReader preview
- Remove isChildFriendly from RecipeCreateRequest (no form field)
- Fix 500 on save: effort values now lowercase, serves/cookTimeMin changed
  from primitive short to nullable Integer to survive omitted fields
- Fix empty categories panel: removed stale tagType=category filter
- Group category tags by type with German headings in recipe form
- Split SuggestionResponse.SuggestionRecipe (no image) from SlotRecipe
- Seed 11 HelloFresh recipes with ingredients, steps and tags (V101)
- Add frontend e2e scaffold, specs and dev yml

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

backend/src/main/java/com/recipeapp/recipe/RecipeService.java

@@ -60,8 +60,10 @@ public class RecipeService {
         Household household = householdRepository.findById(householdId)
                 .orElseThrow(() -> new ResourceNotFoundException("Household not found"));
 
-        Recipe recipe = new Recipe(household, request.name(), request.serves(),
-                request.cookTimeMin(), request.effort(), request.isChildFriendly());
+        Recipe recipe = new Recipe(household, request.name(),
+                request.serves() != null ? request.serves().shortValue() : 0,
+                request.cookTimeMin() != null ? request.cookTimeMin().shortValue() : 0,
+                request.effort(), false);
         recipe.setHeroImageUrl(request.heroImageUrl());
 
         addIngredients(recipe, household, request.ingredients());
@@ -78,10 +80,9 @@ public class RecipeService {
         Household household = recipe.getHousehold();
 
         recipe.setName(request.name());
-        recipe.setServes(request.serves());
-        recipe.setCookTimeMin(request.cookTimeMin());
+        recipe.setServes(request.serves() != null ? request.serves().shortValue() : 0);
+        recipe.setCookTimeMin(request.cookTimeMin() != null ? request.cookTimeMin().shortValue() : 0);
         recipe.setEffort(request.effort());
-        recipe.setChildFriendly(request.isChildFriendly());
         recipe.setHeroImageUrl(request.heroImageUrl());
 
         recipe.getIngredients().clear();