传输等待前台：后台 / 墓碑 iOS 可作可唤醒传输目标 + 发送端等其回前台再传

- 根因：presence 的 online 仅表示有活 SSE，故后台 / 墓碑态 iOS 被判离线、不进传输目标，使前面的后台响应（推送唤醒 + 离线队列）实际无从触发。诉求模型：离线但可唤醒的设备可选作目标；发送端推送唤醒对端、等其回前台上线后再走实时传输（非服务端暂存转发）。
- 后端：transfer.Init 返回 receiverOnline（＝SendTo delivered）；handleTransferInit 回 receiver_online。新增 ListPendingTransfersByReceiver 查询 + Service.RedeliverPendingTo——接收端重连即补发其仍 PENDING 的 transfer:incoming（窗口内），使被唤醒的 iOS 重新 arm P2P answerer（否则发送端 offer 因 p2pHandleSignal 不识未知 peer 而被丢）；sse.go handleEvents 在 hub.Connect 后调用它。
- 发送端 web/transfer.ts：startOutgoingTransfer 按 receiver_online 分流——在线即 beginP2P（原 P2P + fallback 逻辑抽出）；离线则 waitForPeerThenBegin：标 phase=waiting_peer、订阅 presence、对端上线即延 1.2s（待其 arm）再 beginP2P；60s 窗口内不上线则 cancel + FAILED phase=peer_offline。cleanupOutgoing 清理 waitTimer / waitUnsub。TransferPhase 加 waiting_peer / peer_offline + 三语 i18n。
- 目标纳入 + 标记：离线但可唤醒（type 含 ios）的设备可选作传输目标、标「可唤醒」。web DeviceStrip 加 isWakeable（纳入 visible、放开 disabled、标签）；iOS EngineController.sendableDevices 纳入 + isWakeable + sendLabel，三处发送选择器（传输 / 分享 / 收到的文件转发）改用 sendLabel。i18n 加 home.device.wakeable。
- 机制说明（留档）：content-available 静默唤醒不会让挂起的引擎重连 SSE；真正上线＝用户点推送回前台 → 引擎恢复 → SSE 重连 → 后端补发 incoming → arm → 发送端 offer。若 offer 与 arm 抢拍掉了，30s 后 relay 兜底（此时对端已在线）。可唤醒判定用类型启发式（离线 + ios），未加后端 push-sub 查询。
- 测试：service_test 适配 Init 的三返回值。

internal/transfer/service_test.go

@@ -83,7 +83,7 @@ func newTestServiceWithRelay(t *testing.T, r RelayController) *Service {
 
 func TestInit_AllowsZeroByteFile(t *testing.T) {
 	svc := newTestService(t)
-	if _, err := svc.Init(context.Background(), InitParams{
+	if _, _, err := svc.Init(context.Background(), InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "empty.txt", FileSize: 0,
 	}); err != nil {
@@ -93,7 +93,7 @@ func TestInit_AllowsZeroByteFile(t *testing.T) {
 
 func TestInit_PersistsPending(t *testing.T) {
 	svc := newTestService(t)
-	id, err := svc.Init(context.Background(), InitParams{
+	id, _, err := svc.Init(context.Background(), InitParams{
 		UserID:       "alice",
 		SenderName:   "tab-1",
 		ReceiverName: "tab-2",
@@ -129,7 +129,7 @@ func TestInit_RejectsBadInput(t *testing.T) {
 		{UserID: "u", SenderName: "s", ReceiverName: "r", FileName: "f", FileSize: -1},
 	}
 	for i, p := range bad {
-		if _, err := svc.Init(context.Background(), p); err == nil {
+		if _, _, err := svc.Init(context.Background(), p); err == nil {
 			t.Errorf("case %d should error: %+v", i, p)
 		}
 	}
@@ -138,7 +138,7 @@ func TestInit_RejectsBadInput(t *testing.T) {
 func TestTransition_HappyPath_PendingToDone(t *testing.T) {
 	svc := newTestService(t)
 	ctx := context.Background()
-	id, err := svc.Init(ctx, InitParams{
+	id, _, err := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 1024,
 	})
@@ -173,7 +173,7 @@ func TestTransition_HappyPath_PendingToDone(t *testing.T) {
 func TestTransition_FallbackToRelayThenDone(t *testing.T) {
 	svc := newTestService(t)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})
@@ -197,7 +197,7 @@ func TestTransition_RegistersRelayOnFallback(t *testing.T) {
 	fr := &fakeRelay{}
 	svc := newTestServiceWithRelay(t, fr)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "laptop", ReceiverName: "phone",
 		FileName: "f", FileSize: 10,
 	})
@@ -222,7 +222,7 @@ func TestTransition_RelayFullSurfacesUnavailable(t *testing.T) {
 	fr := &fakeRelay{registerErr: errors.New("too many")}
 	svc := newTestServiceWithRelay(t, fr)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})
@@ -242,7 +242,7 @@ func TestTransition_RelayFullSurfacesUnavailable(t *testing.T) {
 func TestTransition_RejectsInvalidJump(t *testing.T) {
 	svc := newTestService(t)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})
@@ -256,7 +256,7 @@ func TestTransition_PendingToActiveAllowed(t *testing.T) {
 	// Race tolerance: sender may call /p2p before receiver's /accept commits.
 	svc := newTestService(t)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})
@@ -269,7 +269,7 @@ func TestTransition_AcceptedToDoneAllowed(t *testing.T) {
 	// Race tolerance: receiver may finish receiving (call /done) before /p2p ever fired.
 	svc := newTestService(t)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})
@@ -284,7 +284,7 @@ func TestTransition_AcceptedToDoneAllowed(t *testing.T) {
 func TestTransition_RejectsForeignUser(t *testing.T) {
 	svc := newTestService(t)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "alice", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})
@@ -307,7 +307,7 @@ func TestExpirePending_CancelsOldSessions(t *testing.T) {
 	old := time.Date(2026, 1, 1, 0, 0, 0, 0, time.UTC)
 	svc.now = func() time.Time { return old }
 
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})
@@ -333,7 +333,7 @@ func TestExpirePending_CancelsOldSessions(t *testing.T) {
 func TestExpirePending_LeavesFreshAlone(t *testing.T) {
 	svc := newTestService(t)
 	ctx := context.Background()
-	id, _ := svc.Init(ctx, InitParams{
+	id, _, _ := svc.Init(ctx, InitParams{
 		UserID: "u", SenderName: "s", ReceiverName: "r",
 		FileName: "f", FileSize: 10,
 	})