fix: use system role for OpenAI Compatible provider when streaming is disabled

- Changed role from "user" to "system" for system prompt in non-streaming mode
- Updated test expectations to match the corrected behavior
- Ensures consistency between streaming and non-streaming modes

Fixes #8215

Author: roomote

src/api/providers/__tests__/openai.spec.ts

@@ -494,7 +494,7 @@ describe("OpenAiHandler", () => {
 				{
 					model: azureOptions.openAiModelId,
 					messages: [
-						{ role: "user", content: systemPrompt },
+						{ role: "system", content: systemPrompt },
 						{ role: "user", content: "Hello!" },
 					],
 				},

src/api/providers/openai.ts

@@ -219,8 +219,8 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 			}
 		} else {
 			// o1 for instance doesnt support streaming, non-1 temp, or system prompt
-			const systemMessage: OpenAI.Chat.ChatCompletionUserMessageParam = {
-				role: "user",
+			const systemMessage: OpenAI.Chat.ChatCompletionSystemMessageParam = {
+				role: "system",
 				content: systemPrompt,
 			}