渠道支持多 API 格式 + 协议全名展示

- Channel 新增 formats(jsonb: chat|responses|messages), 一个渠道可同时声明
  支持 OpenAI Chat Completions / OpenAI Responses API / Anthropic Messages
- 路由改为按渠道声明的 formats 决定直通/转换: 客户端协议在 formats 内直通,
  否则转换为其首选支持格式(chat > messages > responses)
- 兼容旧数据: formats 为空时按 provider 推断(openai→chat+responses, anthropic→messages, compatible→chat)
- 前端: 渠道表/表单展示 API 格式(支持多选), usage 明细显示协议全名
  (OpenAI Chat Completions / OpenAI Responses API / Anthropic Messages)

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

server/internal/proxy/gateway.go

@@ -4,6 +4,7 @@ package proxy
 
 import (
 	"errors"
+	"fmt"
 	"net/http"
 	"strings"
 	"time"
@@ -175,21 +176,6 @@ func (g *Gateway) checkBalance(c *gin.Context, u *store.User) bool {
 // ---------------------------------------------------------------------------
 // 协议分派
 
-// upstreamProtoFor 根据渠道 provider 与客户端协议确定上游协议与路径。
-func upstreamProtoFor(provider, clientProto string) string {
-	switch provider {
-	case store.ChannelProviderAnthropic:
-		return convert.ProtoMessages
-	case store.ChannelProviderOpenAI:
-		if clientProto == convert.ProtoMessages {
-			return convert.ProtoChat
-		}
-		return clientProto
-	default: // compatible：假定 OpenAI Chat 形状
-		return convert.ProtoChat
-	}
-}
-
 func upstreamPath(proto string) string {
 	switch proto {
 	case convert.ProtoMessages:
@@ -209,18 +195,39 @@ type upstreamPlan struct {
 	bodyConv func([]byte) ([]byte, error) // 非流式响应体转换（nil=直通）
 }
 
-// prepareUpstream 计算上游访问计划：协议匹配直通，否则转换。
-func prepareUpstream(provider, clientProto string, body []byte) (*upstreamPlan, error) {
-	up := upstreamProtoFor(provider, clientProto)
-	plan := &upstreamPlan{path: upstreamPath(up), body: body}
-	if up != clientProto {
-		converted, err := convert.ConvertRequest(body, clientProto, up)
+// conversionTarget 决定客户端协议在渠道上的处理方式：
+// 渠道声明支持该协议则直通（返回原协议）；否则转为其首选支持协议（chat > messages > responses）。
+func conversionTarget(formats []string, clientProto string) string {
+	for _, f := range formats {
+		if f == clientProto {
+			return clientProto
+		}
+	}
+	for _, p := range []string{convert.ProtoChat, convert.ProtoMessages, convert.ProtoResponses} {
+		for _, f := range formats {
+			if f == p {
+				return p
+			}
+		}
+	}
+	return ""
+}
+
+// prepareUpstream 计算上游访问计划：渠道声明支持客户端协议则直通，否则转换。
+func prepareUpstream(ch *store.Channel, clientProto string, body []byte) (*upstreamPlan, error) {
+	target := conversionTarget(ch.FormatsEffective(), clientProto)
+	if target == "" {
+		return nil, fmt.Errorf("channel %q declares no supported protocol format", ch.Name)
+	}
+	plan := &upstreamPlan{path: upstreamPath(target), body: body}
+	if target != clientProto {
+		converted, err := convert.ConvertRequest(body, clientProto, target)
 		if err != nil {
 			return nil, err
 		}
 		plan.body = converted
-		plan.lineConv = convert.NewStreamTransformer(up, clientProto)
-		plan.bodyConv = func(b []byte) ([]byte, error) { return convert.ConvertResponse(b, up, clientProto) }
+		plan.lineConv = convert.NewStreamTransformer(target, clientProto)
+		plan.bodyConv = func(b []byte) ([]byte, error) { return convert.ConvertResponse(b, target, clientProto) }
 	}
 	return plan, nil
 }