feat: configurable tool pricing, Sub2API channel, and alpha search billing

Add admin-configurable tool-call prices with cross-provider surcharge
settlement, Sub2API channel support, /v1/alpha/search relay, and usage-log
surcharge UI.

constant/channel.go

@@ -56,6 +56,7 @@ const (
 	ChannelTypeReplicate      = 56
 	ChannelTypeCodex          = 57
 	ChannelTypeAdvancedCustom = 58
+	ChannelTypeSub2API        = 59
 	ChannelTypeDummy          // this one is only for count, do not add any channel after this
 
 )
@@ -120,6 +121,7 @@ var ChannelBaseURLs = []string{
 	"https://api.replicate.com",                 //56
 	"https://chatgpt.com",                       //57
 	"",                                          //58
+	"",                                          //59
 }
 
 var ChannelTypeNames = map[int]string{
@@ -178,6 +180,7 @@ var ChannelTypeNames = map[int]string{
 	ChannelTypeReplicate:      "Replicate",
 	ChannelTypeCodex:          "ChatGPT Subscription (Codex)",
 	ChannelTypeAdvancedCustom: "Advanced Custom",
+	ChannelTypeSub2API:        "Sub2API",
 }
 
 func GetChannelTypeName(channelType int) string {