fix(server): Add explicit JSON response instructions for Cursor prompts

Cursor was writing JSON to files instead of returning it in the response.
Added clear instructions to all Cursor prompts:
1. DO NOT write any files
2. Return ONLY raw JSON in the response
3. No explanations, no markdown, just JSON

Affected routes:
- generate-spec.ts
- generate-features-from-spec.ts
- validate-issue.ts
- generate-suggestions.ts

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/server/src/routes/app-spec/generate-features-from-spec.ts

@@ -125,8 +125,16 @@ IMPORTANT: Do not ask for clarification. The specification is provided above. Ge
 
     const provider = ProviderFactory.getProviderForModel(model);
 
+    // Add explicit instructions for Cursor to return JSON in response
+    const cursorPrompt = `${prompt}
+
+CRITICAL INSTRUCTIONS:
+1. DO NOT write any files. Return the JSON in your response only.
+2. Respond with ONLY a JSON object - no explanations, no markdown, just raw JSON.
+3. Your entire response should be valid JSON starting with { and ending with }. No text before or after.`;
+
     for await (const msg of provider.executeQuery({
-      prompt,
+      prompt: cursorPrompt,
       model,
       cwd: projectPath,
       maxTurns: 250,