Remove blocks as model and switch automatically (#504)

ai/prompts.ts

@@ -9,7 +9,6 @@ export const blocksPrompt = `
   - When explicitly requested to create a document
 
   **When NOT to use \`createDocument\`:**
-  - For short content (<10 lines)
   - For informational/explanatory content
   - For conversational responses
   - When asked to keep it in chat
@@ -24,3 +23,5 @@ export const blocksPrompt = `
 
 export const regularPrompt =
   'You are a friendly assistant! Keep your responses concise and helpful.';
+
+export const systemPrompt = `${regularPrompt}\n\n${blocksPrompt}`;