refactor(xray): drop stale --ant-primary-color fallbacks and hex literals

- RoutingTab .drop-before/.drop-after box-shadow: #1677ff → var(--ant-color-primary)
- OutboundFormModal .random-icon: drop the --ant-primary-color/#1890ff
  pair (the old AntD v4 token name with stale fallback) for the v6
  --ant-color-primary; .danger-icon hex #ff4d4f → var(--ant-color-error).
- XrayPage .restart-icon: same drop of the --ant-primary-color fallback.

These were all leftovers from the AntD v4 → v6 rename — the v6
--ant-color-primary is already populated by ConfigProvider, so the
fallback hex was dead code that would only trigger if AntD wasn't
mounted.

frontend/src/pages/xray/OutboundFormModal.css

@@ -1,12 +1,12 @@
 .random-icon {
   cursor: pointer;
-  color: var(--ant-primary-color, #1890ff);
+  color: var(--ant-color-primary);
   margin-left: 4px;
 }
 
 .danger-icon {
   cursor: pointer;
-  color: #ff4d4f;
+  color: var(--ant-color-error);
   margin-left: 8px;
 }
 

frontend/src/pages/xray/RoutingTab.css

@@ -27,11 +27,11 @@
 }
 
 .drop-before > td {
-  box-shadow: inset 0 2px 0 0 #1677ff;
+  box-shadow: inset 0 2px 0 0 var(--ant-color-primary);
 }
 
 .drop-after > td {
-  box-shadow: inset 0 -2px 0 0 #1677ff;
+  box-shadow: inset 0 -2px 0 0 var(--ant-color-primary);
 }
 
 .row-index {

frontend/src/pages/xray/XrayPage.css

@@ -51,7 +51,7 @@
 .xray-page .restart-icon {
   font-size: 16px;
   cursor: pointer;
-  color: var(--ant-primary-color, #1890ff);
+  color: var(--ant-color-primary);
 }
 
 .xray-page .restart-result {