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/planning/PlanningService.java

@@ -153,7 +153,7 @@ public class PlanningService {
                             plan, candidate, slotDate, config, recentlyCookedIds);
                     double scoreDelta = simulatedScore - currentScore;
                     boolean hasConflict = scoreDelta < 0;
-                    return new SuggestionResponse.SuggestionItem(toSlotRecipe(candidate), scoreDelta, hasConflict);
+                    return new SuggestionResponse.SuggestionItem(toSuggestionRecipe(candidate), scoreDelta, hasConflict);
                 })
                 .sorted((a, b) -> Double.compare(b.scoreDelta(), a.scoreDelta()))
                 .limit(limit)
@@ -422,6 +422,11 @@ public class PlanningService {
                 recipe.getCookTimeMin(), recipe.getHeroImageUrl());
     }
 
+    private SuggestionResponse.SuggestionRecipe toSuggestionRecipe(Recipe recipe) {
+        return new SuggestionResponse.SuggestionRecipe(recipe.getId(), recipe.getName(),
+                recipe.getEffort(), recipe.getCookTimeMin());
+    }
+
     private boolean hasConsecutiveDays(List<LocalDate> days) {
         if (days.size() < 2) return false;
         List<LocalDate> sorted = days.stream().sorted().toList();