fix(billing): surface quota saturation events for admin auditing

Thread int32 saturation clamps from tiered settlement and video task
recompute into the consume/task logs under admin_info, so oversized or
malformed billing inputs stay auditable. Clamp negative audio duration
before token conversion and gate the saturation UI markers on admin.

pkg/billingexpr/billingexpr_test.go

@@ -291,12 +291,9 @@ func TestQuotaRound(t *testing.T) {
 		{999.4999, 999},
 		{999.5, 1000},
 		{1e9 + 0.5, 1e9 + 1},
-		// Oversized expression results must saturate at int32 bounds
-		// instead of wrapping into a negative charge.
+		// Oversized expression results saturate at int32 (delegated to
+		// common.QuotaRound); full saturation coverage lives in common.
 		{3.6893488147419103e19, math.MaxInt32},
-		{-3.6893488147419103e19, math.MinInt32},
-		{math.Inf(1), math.MaxInt32},
-		{math.NaN(), 0},
 	}
 	for _, tt := range tests {
 		got := billingexpr.QuotaRound(tt.in)