feat: 金额 decimal 精确计费、failover 按失败类型封顶、渠道小时桶预聚合、分层守护测试

- 计费：19 个金额字段 float64→decimal.Decimal，DB 列保持 numeric(20,8) 零迁移；
  API 金额仍为 JSON number（MarshalJSONWithoutQuotes），前端零改动
- failover：保留时间预算，新增 OT_PROXY_FAILOVER_CAPS_NET/SERVER/RATE/QUOTA
  按失败类型封顶换渠道次数（429/配额类瞬时失败时间预算形同虚设）
- 预聚合：新增 usage_channel_hourlies（schema v10），记账事务内同步 upsert，
  长窗口渠道统计走桶不再扫明细，spent_last_30d 改扫 usage_daily，v10 一次性回填幂等
- 守护：internal/arch_test.go 用 go/parser 强制分层依赖（fail-closed）

server/internal/api/admin.go

@@ -11,6 +11,7 @@ import (
 	"github.com/gin-gonic/gin"
 	"github.com/openteam/server/internal/pkg/resp"
 	"github.com/openteam/server/internal/store"
+	"github.com/shopspring/decimal"
 	"gorm.io/gorm"
 	"gorm.io/gorm/clause"
 )
@@ -177,14 +178,14 @@ func (h *Handler) AdminAdjustBalance(c *gin.Context) {
 		return
 	}
 	var req struct {
-		Amount float64 `json:"amount" binding:"required"`
-		Remark string  `json:"remark"`
+		Amount decimal.Decimal `json:"amount" binding:"required"`
+		Remark string          `json:"remark"`
 	}
 	if err := c.ShouldBindJSON(&req); err != nil {
 		resp.Fail(c, http.StatusBadRequest, "invalid input: amount required")
 		return
 	}
-	if req.Amount == 0 {
+	if req.Amount.IsZero() {
 		resp.Fail(c, http.StatusBadRequest, "amount must not be zero")
 		return
 	}
@@ -204,7 +205,7 @@ func (h *Handler) AdminAdjustBalance(c *gin.Context) {
 		return tx.Create(&store.BalanceLog{
 			UserID:       u.ID,
 			Change:       req.Amount,
-			BalanceAfter: u.Balance + req.Amount,
+			BalanceAfter: u.Balance.Add(req.Amount),
 			Type:         store.BalanceTypeAdminAdjust,
 			RefID:        ref,
 			Remark:       req.Remark,