feat(frontend): Phase 6-i — xray page scaffold + Advanced JSON tab

The fifth and last legacy page comes online. Tabs are scaffolded with
a-empty placeholders for the structured editors (Basics / Routing /
Outbounds / Balancers / DNS) so navigation is stable; the
Advanced (JSON) tab is fully functional and lets power users edit
the raw xraySetting tree exactly like the legacy CodeMirror pane.

- xray.html + src/xray.js: fifth Vite multi-page entry, mounted as
  XrayPage; vite.config.js routes /panel/xray and /panel/xray/ to it
  through the dev proxy bypass alongside the other pages.
- XrayPage.vue: page chrome with the Save / Restart-xray bar, restart-
  output popover (surfaces /panel/xray/getXrayResult content when
  startup fails), 6 a-tabs, and a textarea-backed Advanced JSON editor.
  CodeMirror is intentionally not pulled in — the textarea works for
  every modern browser and keeps the bundle slim while structured
  editors land in 6-ii through 6-v.
- useXraySetting.js composable: POST /panel/xray/ on mount, mirrors
  the settings-page 1s busy-loop dirty check for both xraySetting
  and outboundTestUrl, and exposes saveAll + restartXray. The dirty
  flag relies on string equality of the pretty-printed JSON, so
  reformat-only edits don't enable Save.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/vite.config.js

@@ -19,6 +19,8 @@ const MIGRATED_ROUTES = {
   '/panel/settings/': '/settings.html',
   '/panel/inbounds': '/inbounds.html',
   '/panel/inbounds/': '/inbounds.html',
+  '/panel/xray': '/xray.html',
+  '/panel/xray/': '/xray.html',
 };
 
 // Build a proxy config that suppresses ECONNREFUSED noise when the Go
@@ -72,6 +74,7 @@ export default defineConfig({
         login: path.resolve(__dirname, 'login.html'),
         settings: path.resolve(__dirname, 'settings.html'),
         inbounds: path.resolve(__dirname, 'inbounds.html'),
+        xray: path.resolve(__dirname, 'xray.html'),
       },
     },
   },