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>

frontend/e2e/startseite.test.ts

@@ -0,0 +1,6 @@
+import { expect, test } from '@playwright/test';
+
+test('Startseite lädt korrekt', async ({ page }) => {
+	await page.goto('/');
+	await expect(page.getByRole('heading', { name: 'Willkommen bei Mealprep' })).toBeVisible();
+});