docs: update LLM provider model and API endpoint in Visualizing_data_with_LLMs vignette

Author: pwwang

vignettes/Visualizing_data_with_LLMs.Rmd

@@ -30,11 +30,11 @@ This vignette demonstrates how to use the `scplotter` package to visualize data
 ```{r, eval = api_key_set}
 # Set up LLM provider
 provider <- tidyprompt::llm_provider_openai(
-    parameters = list(model = "openai/gpt-5.4-nano", stream =
+    parameters = list(model = "deepseek-v4-flash", stream =
       getOption("tidyprompt.stream", TRUE)),
     verbose = getOption("tidyprompt.verbose", TRUE),
-    url = "https://openrouter.ai/api/v1/chat/completions",
-    api_key = Sys.getenv("OPENROUTER_API_KEY")
+    url = "https://api.deepseek.com/chat/completions",
+    api_key = Sys.getenv("OPENAI_API_KEY")
 )
 
 chat <- SCPlotterChat$new(provider = provider)