feat(frontend): Phase 5d-i — settings page shell + dirty tracking

Adds the settings entry as a new Vite multi-page input. Lays down the
shared page chrome (sidebar, save bar, restart, security alert) and the
AllSetting fetch/dirty-poll lifecycle so 5d-ii through 5d-vi can drop
in tab partials without re-implementing it.

- settings.html + src/settings.js: third Vite entry; mounts SettingsPage.
- SettingsPage.vue: page chrome with the legacy two-button save/restart
  bar, conf-alerts banner, and 5 a-tabs (4 always-visible + the formats
  tab gated on subJsonEnable || subClashEnable). Each tab body is an
  a-empty placeholder until 5d-ii…vi fill them in.
- useAllSetting.js composable: POST /panel/setting/all on mount, mirrors
  the legacy 1s busy-loop dirty check via setInterval, and exposes
  fetchAll/saveAll. saveDisabled flips off as soon as the user diverges
  from the server snapshot.
- restartPanel rebuilds the URL (host/port/scheme/base path) from the
  saved settings so users land on the new endpoint after a port or
  cert change.
- models/setting.js: adopts the @/utils alias and a leading file-level
  doc — semantics unchanged.

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

frontend/src/models/setting.js

@@ -1,4 +1,9 @@
-import { ObjectUtil } from '../utils/legacy.js';
+// Mirrors web/assets/js/model/setting.js — every field on this class is
+// round-tripped through `/panel/setting/all` and `/panel/setting/update`,
+// so adding a field here without a matching Go-side change will silently
+// drop it on save. Defaults match the legacy panel.
+
+import { ObjectUtil } from '@/utils';
 
 export class AllSetting {