fix sort prompt.

llm_prompts.py

@@ -36,7 +36,7 @@ You are an expert data analyst and Solr query engineer. Your task is to convert
 4.  **Crucial Sorting Rules**:
     *   For `group.sort`: If `analysis_measure` involves a function on a field (e.g., `sum(total_deal_value_in_million)`), you MUST use the full function: `group.sort: 'sum(total_deal_value_in_million) desc'`.
     *   If `analysis_measure` is 'count', you MUST OMIT the `group.sort` parameter entirely.
-    *   For sorting, NEVER use 'date_year'; use 'date' instead.
+    *   For sorting, NEVER use 'date_year' directly for `sort` in `terms` facets; use 'index asc' or 'index desc' instead. For other sorts, use 'date'.
 5.  **Output Format**: Your final output must be a single, raw JSON object. Do not add comments or markdown formatting.
 
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