refactor: rename systemPromptWithJson to systemPrompt

backend/src/index.ts

@@ -401,7 +401,7 @@ CRITICAL RULES:
 9. NEVER include any closing remarks, sign-offs, or follow-up offers`;
 
   const userInstructions = settings?.journalPrompt;
-  const systemPromptWithJson = userInstructions
+  const systemPrompt = userInstructions
     ? `${defaultPrompt}\n\n${jsonInstruction}\n\nCUSTOM USER INSTRUCTIONS:\n${userInstructions}`
     : `${defaultPrompt}\n\n${jsonInstruction}`;
   
@@ -435,7 +435,7 @@ CRITICAL RULES:
       status: 'pending',
       provider,
       model: model,
-      prompt: `${systemPromptWithJson}\n\n---\n\n${userPrompt}`,
+      prompt: `${systemPrompt}\n\n---\n\n${userPrompt}`,
       request: '',
       response: '',
     },
@@ -455,7 +455,7 @@ CRITICAL RULES:
     
     console.log(`[Journal Generate] AI Provider created: ${aiProvider.provider}`);
     
-    const result = await aiProvider.generate(userPrompt, systemPromptWithJson, { jsonMode: true });
+    const result = await aiProvider.generate(userPrompt, systemPrompt, { jsonMode: true });
     
     if (!result.content) {
       throw new Error('No content generated from AI');