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/_draft_preview.html

@@ -0,0 +1,23 @@
+<div class="msg msg-warning draft-notice">
+  <strong>{{ draft_notice|default:"KI-Entwurf" }} – bitte prüfen.</strong>
+  Noch nichts ist gespeichert. Korrigiere die Felder unten bei Bedarf und tippe dann auf „Speichern“.
+</div>
+{% if ai_draft %}
+<details class="card preview" open>
+  <summary><strong>Vorschau: {{ ai_draft.title|default:"Ohne Titel" }}</strong></summary>
+  {% if ai_draft.ingredients %}
+  <h3>Zutaten</h3>
+  <ul class="ingredients">
+    {% for ing in ai_draft.ingredients %}
+    <li><span class="amount">{% if ing.amount is not None %}{{ ing.amount|floatformat:"-2" }}{% if ing.amount_max is not None %}–{{ ing.amount_max|floatformat:"-2" }}{% endif %}{% endif %} {{ ing.unit }}</span>
+      <span>{% if ing.group %}<span class="muted">{{ ing.group }}: </span>{% endif %}{{ ing.name }}{% if ing.note %}<span class="muted">, {{ ing.note }}</span>{% endif %}</span></li>
+    {% endfor %}
+  </ul>
+  {% endif %}
+  {% if ai_draft.steps %}
+  <h3>Zubereitung</h3>
+  <ol class="steps">{% for step in ai_draft.steps %}<li>{{ step }}</li>{% endfor %}</ol>
+  {% endif %}
+  {% if ai_draft.tags %}<p class="chips">{% for tag in ai_draft.tags %}<span class="chip">#{{ tag }}</span>{% endfor %}</p>{% endif %}
+</details>
+{% endif %}