Fix incorrect string formatting for model payload key

Replaced curly brackets with direct reference to the environment variable in the payload model value. This ensures the correct model is passed dynamically from environment configurations.

src/phoenix_technologies/smd/server.py

@@ -33,7 +33,7 @@ async def summarize_to_words(text: str, title: str, target_word_count: int = 100
         "Content-type": "application/json",
     }
     payload = {
-        "model": {os.getenv('SWISSDOX_SUMMARIZING_MODEL', '')},
+        "model": os.getenv('SWISSDOX_SUMMARIZING_MODEL', ''),
         "messages": [
             {
                 "role": "text summarizer",