feat: 币种输入旁实时显示交易所现价

Shared SymbolLivePrice polls /api/order_defaults on input with debounce; wired to trade, key monitor, trend, and key focus forms.

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

lib/strategy/templates/symbol_live_price_snippet.html

@@ -0,0 +1,10 @@
+{# 币种输入旁实时现价（须加载 symbol_live_price.js） #}
+{% macro symbol_live_price_hint(price_id, symbol_input_id, direction_input_id='') -%}
+<span
+    id="{{ price_id }}"
+    class="symbol-live-price"
+    data-symbol-input="{{ symbol_input_id }}"
+    {% if direction_input_id %}data-direction-input="{{ direction_input_id }}"{% endif %}
+    aria-live="polite"
+>现价：—</span>
+{%- endmacro %}