feat(frontend): Phase 5d-vi — settings Subscription formats tab

Ports the subscription/json partial — paths/URIs for the JSON and
Clash formats plus the four packed-JSON sub-fields: fragment, noises,
mux, and direct routing rules.

- subJsonFragment / subJsonMux / subJsonNoises / subJsonRules are each
  a JSON string on the wire; the tab exposes their fields as computed
  v-models that read+write the underlying JSON. Toggling a top-level
  switch off resets the field to "" (matches legacy semantics).
- Direct routing rules surface the IP and domain entries of the seed
  rule array as multi-select tag inputs; setting/removing tags
  edits the rules array in place rather than rebuilding it from
  scratch, so manually-added rules are preserved.
- Tab is gated on subJsonEnable || subClashEnable in the parent (only
  rendered when the user actually opted into one of those formats).

This closes Phase 5d — full settings page parity with the legacy panel
across all five tabs.

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

frontend/src/pages/settings/SettingsPage.vue

@@ -18,6 +18,7 @@ import GeneralTab from './GeneralTab.vue';
 import SecurityTab from './SecurityTab.vue';
 import TelegramTab from './TelegramTab.vue';
 import SubscriptionGeneralTab from './SubscriptionGeneralTab.vue';
+import SubscriptionFormatsTab from './SubscriptionFormatsTab.vue';
 
 const antdThemeConfig = computed(() => ({
   algorithm: themeState.isDark ? antdTheme.darkAlgorithm : antdTheme.defaultAlgorithm,
@@ -242,7 +243,7 @@ const alertVisible = ref(true);
                         <CodeOutlined />
                         <span>Subscription (Formats)</span>
                       </template>
-                      <a-empty description="Subscription formats — coming in 5d-vi" />
+                      <SubscriptionFormatsTab :all-setting="allSetting" />
                     </a-tab-pane>
                   </a-tabs>
                 </a-col>