feat: 连接设备上限 backstop — 兜住"已登录的超限设备"(#16)

登录挡板只拦新登录,已登录的超限会话(如 pro 已连 5 台)永远不被提示 → 限制形同虚设。
补服务端连接卡点:超限账户连接直接拒,兜住已登录设备(下次一连即被拦,无需重登)。

服务端:
- Entitlement 加 MaxDevices(EntitlementForUser 查 p.max_devices;free 默认 1)
- NodeStore.CountActiveDevices(近 30d 活跃)+ SQLNodeStore/mock 实现
- ConnectNode:activeCount > MaxDevices → 403 {code:DEVICE_LIMIT_EXCEEDED, max_devices}

客户端:
- ConnectApiException 解析 code/max_devices(结构化错误体)
- _connect 遇 DEVICE_LIMIT_EXCEEDED → 置 deviceLimitProvider → 顶层路由弹「移除设备」页
  (设备列表走 devicesProvider),移除到上限内自动放行

后端 go test(store/nodes/httpapi/devices)全过;前端 analyze 干净 + 66 测试过。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/internal/nodes/grpc_test.go

@@ -146,6 +146,10 @@ func (m *mockNodeStore) AccountDayBytes(_ context.Context, _ int64, _ time.Time)
 	return 0, nil
 }
 
+func (m *mockNodeStore) CountActiveDevices(_ context.Context, _ int64, _ time.Time) (int, error) {
+	return 0, nil
+}
+
 func (m *mockNodeStore) UserDeviceByDpUUID(_ context.Context, dpUUID string) (int64, int64, bool, error) {
 	if m.devicesByDpUUID != nil {
 		if ud, ok := m.devicesByDpUUID[dpUUID]; ok {

server/internal/nodes/store.go

@@ -35,6 +35,7 @@ type Entitlement struct {
 	AdGate       bool // true = free plan, require ad unlock + minute quota
 	DailyMinutes sql.NullInt64
 	DailyMB      sql.NullInt64 // 每日综合流量配额(MB, 按账户综合卡); NULL = 不限
+	MaxDevices   int           // 套餐设备上限(free 1 / pro 3 / team 10);0 = 不限
 	ExpiresAt    sql.NullTime  // latest subscription expiry (nil = trial/active)
 }
 
@@ -103,6 +104,10 @@ type NodeStore interface {
 	// date — the basis for the GB 综合配额 connect gate. 0 when no usage yet.
 	AccountDayBytes(ctx context.Context, userID int64, date time.Time) (int64, error)
 
+	// CountActiveDevices counts the user's devices seen since cutoff (active). Used
+	// by the connect device-limit backstop; stale rows are excluded.
+	CountActiveDevices(ctx context.Context, userID int64, cutoff time.Time) (int, error)
+
 	// AccumulateDeviceUsage adds bytes/minutes to usage_device_daily for
 	// (deviceID, date); user_id is carried for per-account rollups/queries.
 	AccumulateDeviceUsage(ctx context.Context, userID, deviceID int64, date time.Time,
@@ -201,7 +206,7 @@ func (s *SQLNodeStore) EntitlementForUser(ctx context.Context, userID int64) (*E
 
 	// Look up the best active subscription.
 	const q = `
-		SELECT p.code, p.ad_gate, p.daily_minutes, p.daily_mb, s.expires_at
+		SELECT p.code, p.ad_gate, p.daily_minutes, p.daily_mb, p.max_devices, s.expires_at
 		FROM subscriptions s
 		JOIN plans p ON p.id = s.plan_id
 		WHERE s.user_id = ? AND s.expires_at > ?
@@ -210,7 +215,7 @@ func (s *SQLNodeStore) EntitlementForUser(ctx context.Context, userID int64) (*E
 	`
 	e := &Entitlement{DpUUID: dpUUID}
 	err := s.db.QueryRowContext(ctx, q, userID, time.Now().UTC()).Scan(
-		&e.PlanCode, &e.AdGate, &e.DailyMinutes, &e.DailyMB, &e.ExpiresAt,
+		&e.PlanCode, &e.AdGate, &e.DailyMinutes, &e.DailyMB, &e.MaxDevices, &e.ExpiresAt,
 	)
 	if err == sql.ErrNoRows {
 		// No active subscription → free plan defaults (mirrors the free plan seed).
@@ -218,6 +223,7 @@ func (s *SQLNodeStore) EntitlementForUser(ctx context.Context, userID int64) (*E
 		e.AdGate = true
 		e.DailyMinutes = sql.NullInt64{Valid: true, Int64: 10}
 		e.DailyMB = sql.NullInt64{Valid: true, Int64: 500}
+		e.MaxDevices = 1
 		return e, nil
 	}
 	if err != nil {
@@ -467,6 +473,19 @@ func (s *SQLNodeStore) AccountDayBytes(ctx context.Context, userID int64, date t
 	return total.Int64, nil
 }
 
+// CountActiveDevices counts the user's devices seen within the active window
+// (last_seen > cutoff). Mirrors devices.Store.CountActiveDevices for the connect
+// backstop; stale/never-seen rows are excluded.
+func (s *SQLNodeStore) CountActiveDevices(ctx context.Context, userID int64, cutoff time.Time) (int, error) {
+	var n int
+	if err := s.db.QueryRowContext(ctx,
+		`SELECT COUNT(1) FROM devices WHERE user_id=? AND last_seen IS NOT NULL AND last_seen > ?`,
+		userID, cutoff.UTC()).Scan(&n); err != nil {
+		return 0, fmt.Errorf("nodes.SQLNodeStore.CountActiveDevices: %w", err)
+	}
+	return n, nil
+}
+
 // AccumulateUsage adds bytes/minutes to usage_daily for the given user and date.
 func (s *SQLNodeStore) AccumulateUsage(
 	ctx context.Context, userID int64, date time.Time,