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/dto/RecipeCreateRequest.java

@@ -6,13 +6,13 @@ import java.math.BigDecimal;
 import java.util.List;
 import java.util.UUID;
 
+
 public record RecipeCreateRequest(
         @NotBlank @Size(max = 200) String name,
-        @Min(1) @Max(20) short serves,
-        @Min(0) short cookTimeMin,
+        Integer serves,
+        Integer cookTimeMin,
         @NotBlank @Pattern(regexp = "easy|medium|hard") String effort,
-        boolean isChildFriendly,
-        @Size(max = 500) String heroImageUrl,
+        String heroImageUrl,
         @NotEmpty @Valid List<IngredientEntry> ingredients,
         @Valid List<StepEntry> steps,
         @NotEmpty List<UUID> tagIds