feat(ui): enforce shared page shell contract

frontend/src/components/Layout.vue

@@ -195,7 +195,9 @@
         <div class="content-wrapper">
           <router-view v-slot="{ Component }">
             <transition name="fade-transform" mode="out-in">
-              <component :is="Component" />
+              <div class="ctms-route-shell">
+                <component :is="Component" />
+              </div>
             </transition>
           </router-view>
         </div>
@@ -704,6 +706,10 @@ const onCommand = (cmd: string) => {
   background: #f7f8fb;
 }
 
+.ctms-route-shell {
+  min-height: 100%;
+}
+
 /* 过渡动画 */
 .fade-transform-enter-active,
 .fade-transform-leave-active {

frontend/src/styles/unified-page.css

@@ -9,6 +9,22 @@
   --unified-muted-color: #6f84a8;
 }
 
+.ctms-page-shell {
+  padding: 16px 20px 20px;
+}
+
+.ctms-page-header-row {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  gap: 12px;
+}
+
+.ctms-page-content-grid {
+  display: grid;
+  gap: 12px;
+}
+
 .unified-shell {
   background: var(--unified-shell-bg);
   border: 0;