新增: 依赖图环形检测 + PNG 导出 + 任务列表真实总数

- 后端 detect_module_cycles IPC(DFS 三色标记法检测环形依赖)
- 前端环检测按钮:高亮参与环的节点(红色边框)
- 图导出 PNG(X6 toPNG 回调模式)
- 后端 count_tasks IPC + 前端 taskApi.count()
- 任务列表所有筛选/搜索/排序/翻页均拉真实 total

src/views/Tasks.vue

@@ -252,7 +252,10 @@ watch(searchKeyword, () => {
   _searchTimer = setTimeout(() => {
     page.value = 1
     loading.value = true
-    store.loadTasks(buildTaskQuery()).finally(() => { loading.value = false })
+    Promise.all([
+      store.loadTasks(buildTaskQuery()),
+      taskApi.count(buildTaskQuery()).then(n => totalTasks.value = n),
+    ]).finally(() => { loading.value = false })
   }, 300)
 })
 
@@ -383,20 +386,29 @@ watch(activeProject, () => {
   store.setActiveTaskProject(activeProject.value)
   page.value = 1
   loading.value = true
-  store.loadTasks(buildTaskQuery()).finally(() => { loading.value = false })
+  Promise.all([
+    store.loadTasks(buildTaskQuery()),
+    taskApi.count(buildTaskQuery()).then(n => totalTasks.value = n),
+  ]).finally(() => { loading.value = false })
 })
 
 watch(activeStatus, () => {
   store.setActiveTaskStatus(activeStatus.value)
   page.value = 1
   loading.value = true
-  store.loadTasks(buildTaskQuery()).finally(() => { loading.value = false })
+  Promise.all([
+    store.loadTasks(buildTaskQuery()),
+    taskApi.count(buildTaskQuery()).then(n => totalTasks.value = n),
+  ]).finally(() => { loading.value = false })
 })
 
 watch(sortBy, () => {
   page.value = 1
   loading.value = true
-  store.loadTasks(buildTaskQuery()).finally(() => { loading.value = false })
+  Promise.all([
+    store.loadTasks(buildTaskQuery()),
+    taskApi.count(buildTaskQuery()).then(n => totalTasks.value = n),
+  ]).finally(() => { loading.value = false })
 })
 
 // Ctrl+N 新建 / Ctrl+F 搜索(桌面快捷键)
@@ -415,7 +427,11 @@ onMounted(async () => {
   store.setActiveTaskStatus(activeStatus.value)
   loading.value = true
   try {
-    await Promise.all([store.loadProjects(), store.loadTasks()])
+    await Promise.all([
+      store.loadProjects(),
+      store.loadTasks(),
+      taskApi.count().then(n => totalTasks.value = n),
+    ])
   } finally {
     loading.value = false
   }