代理: 鉴权支持 Anthropic x-api-key 头

Claude Code / Anthropic SDK 用 x-api-key 头而不是 Authorization:
Bearer，缺失 Authorization 时回退读取 x-api-key，错误文案同步提示两种方式

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

server/internal/proxy/gateway.go

@@ -135,8 +135,12 @@ func (g *Gateway) Auth(c *gin.Context) {
 	auth := c.GetHeader("Authorization")
 	key := strings.TrimPrefix(auth, "Bearer ")
 	key = strings.TrimSpace(key)
+	if key == "" {
+		// Anthropic 客户端（Claude Code / SDK）用 x-api-key 头而不是 Authorization
+		key = strings.TrimSpace(c.GetHeader("x-api-key"))
+	}
 	if !apikey.Valid(key) {
-		apiError(c, http.StatusUnauthorized, "invalid_api_key", "Invalid API key format. Expected: Bearer sk-...")
+		apiError(c, http.StatusUnauthorized, "invalid_api_key", "Invalid API key format. Expected: Authorization: Bearer sk-... or x-api-key: sk-...")
 		c.Abort()
 		return
 	}