refactor(projects): assign + assign-batch 合并为单路由, 子页面 v-if 区分

- router 删 /assign-batch 路由, 仅保留 /assign (单条/批量都走)
- Projects.vue openAssign() 2 个 push 路径统一为 /manager/projects/assign
- 子页面面包屑加 v-if 批量模式 tag (橙色 badge 标识)
- 单/批模式区分完全靠 query.projectId vs query.projectIds + 子页面内 v-if/v-else 区块 (info-bar / 实时校验栏)

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

ry-vue3/src/views/manager/Projects.vue

@@ -467,12 +467,14 @@ function openAssign() {
     ElMessage.warning('请先勾选项目')
     return
   }
-  // 跳转独立子页面: 单条 vs 批量
+  // 跳转独立子页面 /manager/projects/assign, 单条 vs 批量通过 query 区分:
+  //   单条: ?projectId=X       → 子页面 v-if 单条分支
+  //   批量: ?projectIds=1,2,3   → 子页面 v-else 批量分支
   if (selection.value.length === 1) {
     router.push({ path: '/manager/projects/assign', query: { projectId: selection.value[0].projectId } })
   } else {
     const ids = selection.value.map(r => r.projectId).join(',')
-    router.push({ path: '/manager/projects/assign-batch', query: { projectIds: ids } })
+    router.push({ path: '/manager/projects/assign', query: { projectIds: ids } })
   }
 }
 function openBatch(kind) {