Add tabs for all, own and favourite recipes

- Tabs "Alle", "Eigene Rezepte", "Favoriten" above the recipe list;
  search and tag filters stay within the active tab
- Menu link to own recipes; empty states per tab
- Fix recipe card images rendering portrait instead of 4:3

Co-Authored-By: Claude Opus 5.5 <[email protected]>

templates/base.html

@@ -22,6 +22,7 @@
       <summary aria-label="Menü">☰</summary>
       <nav>
         <a href="{% url 'recipes:list' %}">Rezepte</a>
+        <a href="{% url 'recipes:list' %}?ansicht=meine">Eigene Rezepte</a>
         <a href="{% url 'recipes:list' %}?ansicht=favoriten">Favoriten</a>
         <a href="{% url 'recipes:import' %}">Importieren</a>
         <a href="{% url 'accounts:profile' %}">Mein Konto</a>