fix(cache): 存量空/url 策略规范为 all，避免静默收窄

评审修复：enabled 且 policy 为空或 url 时，写入/展示/快照/渲染均映射为 all，
保证旧站点宽缓存范围不变；新建 UI 仍显式提交 static 作为推荐默认。

frontend/app/(main)/proxy-routes/components/helpers.ts

@@ -335,12 +335,17 @@ export function buildPayloadFromRoute(
     limit_conn_per_ip: route.limit_conn_per_ip,
     limit_rate: route.limit_rate,
     cache_enabled: route.cache_enabled,
-    cache_policy:
-      !route.cache_policy || route.cache_policy === 'url'
-        ? route.cache_policy === 'url'
-          ? 'all'
-          : 'static'
-        : route.cache_policy,
+    cache_policy: (() => {
+      if (!route.cache_enabled) {
+        return 'static';
+      }
+      const policy = (route.cache_policy || '').trim();
+      // Legacy empty/url → all (same as backend displayCachePolicy).
+      if (!policy || policy === 'url' || policy === 'all') {
+        return 'all';
+      }
+      return policy;
+    })(),
     cache_rules: route.cache_rule_list ?? [],
     custom_headers: route.custom_header_list ?? [],
     basic_auth_enabled: route.basic_auth_enabled,