feat(whatsapp): QWEN primary AI backend, Hermes fallback, conversation history, vehicle persistence, demo prompts

- Add QWEN (qwen3.6) as primary AI backend with short system prompt
- Hermes remains as fallback with 45s timeout
- Increase QWEN timeout to 35s, max_tokens to 4000
- Add conversation history loading from whatsapp_messages (last 4 msgs)
- Persist detected vehicle in whatsapp_sessions table
- Add 'limpiar chat' / 'nuevo chat' / 'reset' commands to clear history
- Fix CSS conflict: rename whatsapp chat-panel classes to wa-chat-panel
- Fix JS ID conflicts with chat.js widget (waChatPanel, waChatMessages, etc.)
- Improve no-stock response: conversational with alternatives
- Split search_query by | for multi-part lookups
- Add DEMO_PROMPTS.md and DEMO_PROMPTS_V2.md

pos/services/inventory_engine.py

@@ -96,12 +96,13 @@ def get_stock_bulk(conn, branch_id=None):
 
 
 def record_operation(conn, inventory_id, branch_id, operation_type, quantity,
-                     reference_id=None, reference_type=None, cost_at_time=None, notes=None):
+                     reference_id=None, reference_type=None, cost_at_time=None,
+                     notes=None, employee_id=None):
     """Record a single inventory operation. Does NOT commit — caller controls transaction.
 
     Args:
         quantity: positive for entries (PURCHASE, RETURN, INITIAL), negative for exits (SALE)
-        operation_type: SALE, PURCHASE, RETURN, ADJUST, TRANSFER, INITIAL
+        operation_type: SALE, PURCHASE, RETURN, ADJUST, TRANSFER, INITIAL, QUOTE_RESERVE, QUOTE_RELEASE
     """
     cur = conn.cursor()
     cur.execute("""
@@ -113,7 +114,7 @@ def record_operation(conn, inventory_id, branch_id, operation_type, quantity,
     """, (
         inventory_id, branch_id, operation_type, quantity,
         reference_id, reference_type, cost_at_time,
-        _safe_g('employee_id'),
+        employee_id if employee_id is not None else _safe_g('employee_id'),
         _safe_g('device_id'),
         notes
     ))