feat(stylist): add strict reminder before LLM call

Inject English reminder message right before LLM call to force:
- All SKUs in response MUST be in product_ids
- Combo/set queries MUST return 5+ products
- Pick from suggest_items/ai_matches if tool returns <5
- Final self-check for (XXXXX) patterns
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/agent/lead_stage_agent/graph.py

@@ -592,6 +592,14 @@ class LeadStageGraph:
                 HumanMessage(content="=== KHÔNG CÓ TOOL RESULT === (Khách chào hỏi hoặc câu hỏi chung)")
             )
 
+        # Strict reminder before LLM call
+        stylist_messages.append(HumanMessage(content="""REMINDER - MUST FOLLOW:
+1. List ALL SKUs mentioned in your response in `product_ids` array.
+2. For combo/set queries: MUST return 5+ products (TOP + BOTTOM).
+3. If tool returns <5 items, PICK MORE from `suggest_items`/`ai_matches`.
+4. Final check: Scan your response for (XXXXX) patterns, ensure ALL are in `product_ids`.
+Output ONLY JSON, no extra text!"""))
+
         # ── LLM Call: Parse JSON from text (Claude returns text, not structured) ──
         # ── LLM Call: Parse JSON from text (Claude returns text, not structured) ──
         start = time.time()