refactor(admin): retire settings migration and compat menu demotion

Stop auto-running AKSRT_Settings_Migration, drop multi-option settings
merge and Zibll favicon aliases, remove the migration tools entry from
menus/schema, flatten admin sections so pages are not demoted into a
compat bag, and retire the migration-status payload for leftover SPA
routes after a full admin rebuild.

assets/admin/src/pages/theme/ThemeInfoPage.vue

@@ -116,10 +116,6 @@
             <FaIcon icon="fas fa-exchange-alt" :size="16" />
             <span>导入导出</span>
           </router-link>
-          <router-link to="/tools/migration" class="aksrt-theme-info__link">
-            <FaIcon icon="fas fa-database" :size="16" />
-            <span>迁移状态</span>
-          </router-link>
         </div>
       </n-card>
     </template>