Add Enable/Disable Toggle for Xray Routing Rules (#5296)

* feat: add enable/disable toggle for xray routing rules

* fix(routing): never let the internal api rule be disabled

The Enable/Disable toggle could strip the stats api rule: its table
switch was locked, but the rule-form modal's Enable dropdown was not,
and stripDisabledRules had no api-rule guard (EnsureStatsRouting's
delete only runs when the api rule isn't already first). A disabled
api rule then dropped out of the generated config and broke traffic
accounting.

- stripDisabledRules now always keeps the api rule, even if marked
  disabled, and strips the panel-only enabled key from every rule
- extract isApiRule helper (backend + frontend) and reuse it across
  the table switch, card switch, and form modal
- disable the form-modal Enable dropdown for the api rule
- add stripDisabledRules tests covering the api-rule survival path

---------

Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

frontend/src/pages/xray/routing/RoutingTab.css

@@ -235,3 +235,7 @@
   text-align: center;
 }
 
+.rule-disabled {
+  opacity: 0.5;
+  filter: grayscale(1);
+}