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_vehicle_compat.py

@@ -403,3 +403,56 @@ def save_qwen_fitment(tenant_conn, inventory_id, fitment_result):
     tenant_conn.commit()
     cur.close()
     return inserted
+
+
+def get_inventory_by_vehicle(tenant_conn, master_conn, mye_id, branch_id=None):
+    """Return local inventory items compatible with a given vehicle (MYE).
+
+    Args:
+        tenant_conn: Connection to tenant DB.
+        master_conn: Connection to master DB (kept for API consistency).
+        mye_id: model_year_engine_id.
+        branch_id: Optional branch filter for stock.
+
+    Returns:
+        List of tuples: (id, part_number, name, brand, price_1, price_2, price_3,
+                          image_url, description, stock)
+    """
+    cur = tenant_conn.cursor()
+
+    if branch_id:
+        # Stock for specific branch
+        cur.execute("""
+            SELECT i.id, i.part_number, i.name, i.brand,
+                   i.price_1, i.price_2, i.price_3,
+                   i.image_url, i.description,
+                   COALESCE(s.stock, 0) as stock
+            FROM inventory i
+            JOIN inventory_vehicle_compat ivc ON ivc.inventory_id = i.id
+            LEFT JOIN inventory_stock_summary s
+                ON s.inventory_id = i.id AND s.branch_id = %s
+            WHERE ivc.model_year_engine_id = %s
+              AND i.is_active = true
+            ORDER BY i.name
+        """, (branch_id, mye_id))
+    else:
+        # Total stock across all branches
+        cur.execute("""
+            SELECT i.id, i.part_number, i.name, i.brand,
+                   i.price_1, i.price_2, i.price_3,
+                   i.image_url, i.description,
+                   COALESCE(SUM(s.stock), 0) as stock
+            FROM inventory i
+            JOIN inventory_vehicle_compat ivc ON ivc.inventory_id = i.id
+            LEFT JOIN inventory_stock_summary s ON s.inventory_id = i.id
+            WHERE ivc.model_year_engine_id = %s
+              AND i.is_active = true
+            GROUP BY i.id, i.part_number, i.name, i.brand,
+                     i.price_1, i.price_2, i.price_3,
+                     i.image_url, i.description
+            ORDER BY i.name
+        """, (mye_id,))
+
+    rows = cur.fetchall()
+    cur.close()
+    return rows