feat(channel): 为 Telegram 和微信企业号添加代理支持

新增 HTTP 客户端工厂函数以支持通过代理发送请求，代理地址可在频道配置中设置。同时修复了微信企业号 TokenStore 更新时代理地址未同步的问题，并确保 Token 存储键值包含代理信息以避免冲突。

channel/http-client.go

@@ -0,0 +1,63 @@
+package channel
+
+import (
+	"context"
+	"errors"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"golang.org/x/net/proxy"
+)
+
+func newHTTPClient(proxyAddress string, timeout time.Duration) (*http.Client, error) {
+	transport, err := newHTTPTransport(proxyAddress)
+	if err != nil {
+		return nil, err
+	}
+	return &http.Client{
+		Timeout:   timeout,
+		Transport: transport,
+	}, nil
+}
+
+func newHTTPTransport(proxyAddress string) (*http.Transport, error) {
+	base, ok := http.DefaultTransport.(*http.Transport)
+	if !ok {
+		return &http.Transport{}, nil
+	}
+	transport := base.Clone()
+	proxyAddress = strings.TrimSpace(proxyAddress)
+	if proxyAddress == "" {
+		transport.Proxy = nil
+		return transport, nil
+	}
+	if !strings.Contains(proxyAddress, "://") {
+		proxyAddress = "http://" + proxyAddress
+	}
+	u, err := url.Parse(proxyAddress)
+	if err != nil {
+		return nil, err
+	}
+	switch strings.ToLower(u.Scheme) {
+	case "http", "https":
+		transport.Proxy = http.ProxyURL(u)
+		return transport, nil
+	case "socks5", "socks5h":
+		normalized := *u
+		normalized.Scheme = "socks5"
+		dialer, err := proxy.FromURL(&normalized, proxy.Direct)
+		if err != nil {
+			return nil, err
+		}
+		transport.Proxy = nil
+		transport.DialContext = func(ctx context.Context, network, addr string) (net.Conn, error) {
+			return dialer.Dial(network, addr)
+		}
+		return transport, nil
+	default:
+		return nil, errors.New("unsupported proxy scheme: " + strings.TrimSpace(u.Scheme))
+	}
+}