Replace deprecated preview image model (home-assistant#158048)

Author: Shulyaka

homeassistant/components/google_generative_ai_conversation/const.py

@@ -23,7 +23,7 @@
 RECOMMENDED_CHAT_MODEL = "models/gemini-2.5-flash"
 RECOMMENDED_STT_MODEL = RECOMMENDED_CHAT_MODEL
 RECOMMENDED_TTS_MODEL = "models/gemini-2.5-flash-preview-tts"
-RECOMMENDED_IMAGE_MODEL = "models/gemini-2.5-flash-image-preview"
+RECOMMENDED_IMAGE_MODEL = "models/gemini-2.5-flash-image"
 CONF_TEMPERATURE = "temperature"
 RECOMMENDED_TEMPERATURE = 1.0
 CONF_TOP_P = "top_p"