Add phase 4: AI cleanup and photo/text import via OpenAI

- recipes/ai.py: Chat Completions with strict JSON schema (Structured
  Outputs), Pydantic re-validation, plausibility clamping, prompt treats
  input as data only
- "Mit KI aufbereiten" on create/edit form returns an editable draft
- Import page: photo/screenshot (vision, downscaled JPEG, not stored) and
  pasted text; drafts pre-fill the recipe form with a preview
- Clear UI messages for timeout, rate limit, quota, auth, model and
  connection errors; without OPENAI_API_KEY AI features show a notice
- Optional per-user and global daily AI limits (default unlimited)
- Tests for response parsing, schema strictness, error mapping, views

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

templates/recipes/list.html

@@ -3,7 +3,10 @@
 {% block content %}
 <div class="page-head">
   <h1>Rezepte</h1>
-  <a class="button" href="{% url 'recipes:create' %}">+ Neu</a>
+  <div class="head-actions">
+    <a class="button secondary" href="{% url 'recipes:import' %}">Import</a>
+    <a class="button" href="{% url 'recipes:create' %}">+ Neu</a>
+  </div>
 </div>
 
 <form method="get" class="search" role="search">