Fix Gate key_focus 500 from invalid Jinja startswith filter.

Use (value|upper).startswith(...) so symbol whitelist select works when default is BTC/USDT.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/strategy/templates/trade_policy_fields.html

@@ -7,7 +7,7 @@
 <select name="{{ name }}" id="{{ id }}" {% if required %}required{% endif %} class="trade-policy-symbol-select">
     <option value="">选择币种</option>
     {% for sym in trade_policy.symbol_whitelist %}
-    <option value="{{ sym }}" {% if value and (value|upper == sym or value|upper.startswith(sym ~ '/')) %}selected{% endif %}>{{ sym }}/USDT</option>
+    <option value="{{ sym }}" {% if value and ((value|upper) == sym or (value|upper).startswith(sym ~ '/')) %}selected{% endif %}>{{ sym }}/USDT</option>
     {% endfor %}
 </select>
 {% else %}