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]>

.env.example

@@ -57,3 +57,14 @@ IMAGE_MAX_PER_RECIPE=10
 # --- Kommentare ------------------------------------------------------------------
 # Maximal so viele Kommentare pro Nutzer und Stunde (0 = unbegrenzt)
 COMMENT_RATE_LIMIT_PER_HOUR=30
+
+# --- KI (OpenAI) -------------------------------------------------------------------
+# Ohne Key funktioniert alles außer den KI-Funktionen.
+OPENAI_API_KEY=
+OPENAI_MODEL=gpt-5-mini
+# Nur für Reasoning-Modelle (gpt-5*, o*): minimal|low|medium|high. Für andere Modelle leer lassen.
+OPENAI_REASONING_EFFORT=low
+OPENAI_TIMEOUT=90
+# Optionale Kostenbremse: KI-Aufrufe pro Tag (0 = unbegrenzt)
+AI_RATE_LIMIT_PER_USER_PER_DAY=0
+AI_RATE_LIMIT_GLOBAL_PER_DAY=0