refactor(task): replace init registration with bootstrap wiring

Introduce internal/bootstrap as the composition root with sync.Once
guards for task handler registration and push listener wiring. Replace
the single OnTaskCompleted global hook with multi-subscriber handlers
and remove init()-driven side effects from worker, admin task, and push.

internal/task/executor.go

@@ -26,8 +26,16 @@ import (
 // handlerRegistry 已注册的任务处理器
 var handlerRegistry = make(map[string]TaskHandler)
 
-// OnTaskCompleted is a hook called when a task execution completes.
-var OnTaskCompleted func(ctx context.Context, execution *model.TaskExecution, result *TaskResult, execErr error)
+// CompletedHandler is called when a task execution completes.
+type CompletedHandler func(ctx context.Context, execution *model.TaskExecution, result *TaskResult, execErr error)
+
+var taskCompletedHandlers []CompletedHandler
+
+// OnTaskCompleted registers a handler for task completion events.
+// Handlers must be registered during application bootstrap before processing tasks.
+func OnTaskCompleted(handler CompletedHandler) {
+	taskCompletedHandlers = append(taskCompletedHandlers, handler)
+}
 
 // RegisterHandler 注册任务处理器
 // 传入任务类型标识（对应 constants.go 中的 AsynqTask 常量）和 TaskHandler 实现
@@ -405,9 +413,17 @@ func completeTaskExecution(ctx context.Context, execution *model.TaskExecution,
 		}
 	}
 
-	if OnTaskCompleted != nil {
-		asyncCtx := context.WithoutCancel(ctx)
-		go OnTaskCompleted(asyncCtx, execution, result, execErr)
+	notifyTaskCompleted(ctx, execution, result, execErr)
+}
+
+func notifyTaskCompleted(ctx context.Context, execution *model.TaskExecution, result *TaskResult, execErr error) {
+	if len(taskCompletedHandlers) == 0 {
+		return
+	}
+
+	asyncCtx := context.WithoutCancel(ctx)
+	for _, handler := range taskCompletedHandlers {
+		go handler(asyncCtx, execution, result, execErr)
 	}
 }
 

internal/task/scheduler/scheduler.go

@@ -11,6 +11,7 @@ import (
 	"syscall"
 	"time"
 
+	"github.com/Rain-kl/Wavelet/internal/bootstrap"
 	"github.com/Rain-kl/Wavelet/internal/model"
 	"github.com/Rain-kl/Wavelet/internal/task"
 	"github.com/Rain-kl/Wavelet/pkg/logger"
@@ -32,6 +33,8 @@ func GetAsynqClient() *asynq.Client {
 
 // StartScheduler 启动调度器 (该函数阻塞，直到调度器退出)
 func StartScheduler() error {
+	bootstrap.RegisterScheduler()
+
 	var err error
 	schedulerOnce.Do(func() {
 		quitChan = make(chan struct{})

internal/task/worker/worker.go

@@ -7,22 +7,18 @@ package worker
 import (
 	"time"
 
+	"github.com/Rain-kl/Wavelet/internal/bootstrap"
 	"github.com/Rain-kl/Wavelet/internal/config"
 	"github.com/Rain-kl/Wavelet/internal/task"
-	taskhandlers "github.com/Rain-kl/Wavelet/internal/task/handlers"
 	"github.com/hibiken/asynq"
 )
 
 // workerShutdownTimeout Worker 优雅关闭超时时间
 const workerShutdownTimeout = 3 * time.Minute
 
-func init() {
-	// 注册所有任务处理器
-	taskhandlers.Register()
-}
-
 // StartWorker 启动任务处理服务器
 func StartWorker() error {
+	bootstrap.RegisterWorker()
 	asynqServer := asynq.NewServer(
 		task.RedisOpt,
 		asynq.Config{