Add phase 5: link import, Instagram fallback and share target

- SSRF-safe fetcher: public IPs only, connects to the checked address,
  redirects re-validated, size/time limits, honest user agent
- schema.org/Recipe JSON-LD extraction (graphs, HowToSections, ISO
  durations, yields, keywords, images) without extra dependencies;
  AI fallback on plain page text when no structured recipe exists
- Instagram: one login-free request to the public embed page; when
  Instagram withholds the caption, the import page explains how to paste
  the text or import a screenshot instead
- Suggested source photo can be downloaded and attached on save
- Text import works without AI (text becomes the description)
- Installable PWA with manifest, icons and Android share target
- Offline tests for SSRF rules, parsers, Instagram and import views

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

templates/base.html

@@ -6,6 +6,11 @@
   <meta name="theme-color" content="#b4532a">
   <meta name="robots" content="noindex, nofollow">
   <title>{% block title %}Kochbuch{% endblock %} · Kochbuch</title>
+  <link rel="manifest" href="{% url 'core:manifest' %}">
+  <link rel="icon" type="image/png" href="{% static 'icons/favicon.png' %}">
+  <link rel="apple-touch-icon" href="{% static 'icons/apple-touch-icon.png' %}">
+  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="apple-mobile-web-app-title" content="Kochbuch">
   <link rel="stylesheet" href="{% static 'css/app.css' %}">
   <script src="{% static 'js/app.js' %}" defer></script>
 </head>
@@ -17,6 +22,8 @@
       <summary aria-label="Menü">☰</summary>
       <nav>
         <a href="{% url 'recipes:list' %}">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>
         {% if user.is_admin %}
         <a href="{% url 'accounts:admin_users' %}">Nutzer verwalten</a>