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]>

static/css/app.css

@@ -271,3 +271,12 @@ h3 { font-size: 1rem; margin: 1rem 0 0.25rem; color: var(--muted); }
 .checklist input:checked + span { opacity: 0.45; text-decoration: line-through; }
 .steps-big { font-size: 1.25rem; line-height: 1.55; }
 .step-no { font-weight: 700; color: var(--accent); }
+
+/* --- Import & drafts ---------------------------------------------------------------- */
+.head-actions { display: flex; gap: 0.5rem; }
+.small { font-size: 0.85rem; }
+.draft-notice { margin-bottom: 1rem; }
+.preview summary { cursor: pointer; }
+.preview .ingredients .amount { flex-basis: 5.5rem; }
+button[disabled] { opacity: 0.6; cursor: progress; }
+code { font-size: 0.9em; }