fix: recipe errors now show specific cause instead of generic 'connection error'

- PHP generateRecipeStream: wrap entire body in try/catch(\Throwable) to catch
  any PHP fatal/exception mid-stream and send it as a proper SSE error event
- PHP: curl timeout raised 60s→90s; capture curl errno/errmsg on failure
- PHP: HTTP error messages now include a human-readable status label
  (e.g. 'Quota API esaurita (429)', 'Nessuna risposta da Gemini (cURL: ...)')
- JS catch block: show err.message alongside error.connection so the actual
  JS network error (NetworkError, AbortError, etc.) is visible
- JS no-recipe+no-error path: show recipes.stream_interrupted instead of
  generic error.connection
- Translation: added recipes.stream_interrupted in it/en/de

translations/de.json

@@ -367,6 +367,7 @@
     "steps_title": "👨‍🍳 Zubereitung",
     "no_steps": "Keine Zubereitungsschritte verfügbar",
     "generate_error": "Fehler bei der Generierung",
+    "stream_interrupted": "Generierung unterbrochen (unvollstaendige Antwort vom Server). Protokolle pruefen oder erneut versuchen.",
     "persons_short": "Pers.",
     "use_ingredient_title": "Zutat verwenden",
     "recipe_qty_label": "Rezept",