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/entity/Recipe.java

@@ -36,7 +36,7 @@ public class Recipe {
     @Column(name = "is_child_friendly", nullable = false)
     private boolean isChildFriendly;
 
-    @Column(name = "hero_image_url", length = 500)
+    @Column(name = "hero_image_url", columnDefinition = "text")
     private String heroImageUrl;
 
     @Column(name = "deleted_at")