Agent plans tasks by referring to its own prompt. (#9315)

### What problem does this PR solve?

Fixes the issue in the analyze_task execution flow where the Lead Agent
was not utilizing its own sys_prompt during task analysis, resulting in
incorrect or incomplete task planning.
https://github.com/infiniflow/ragflow/issues/9294
### Type of change

- [x] New Feature (non-breaking change which adds functionality)

rag/prompts/analyze_task_user.md

@@ -4,6 +4,9 @@ Task: {{ task }}
 
 Context: {{ context }}
 
+**Agent Prompt**
+{{ agent_prompt }}
+
 **Analysis Requirements:**
 1. Is it just a small talk? (If yes, no further plan or analysis is needed)
 2. What is the core objective of the task?