feat(update): 添加在线更新和定价数据获取的代理支持

针对国内服务器访问 GitHub 困难的问题，为在线更新和定价数据获取功能添加代理支持。

主要变更：
- 新增 update.proxy_url 配置项，支持 http/https/socks5/socks5h 协议
- 修改 GitHubReleaseClient 和 PricingRemoteClient 支持代理配置
- 更新 Wire 依赖注入，通过 Provider 函数传递配置
- 更新 Docker 配置文件，支持通过 UPDATE_PROXY_URL 环境变量设置代理

配置示例：
  update:
    proxy_url: "http://127.0.0.1:7890"

Docker 环境变量：
  UPDATE_PROXY_URL=http://host.docker.internal:7890

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/internal/repository/pricing_service.go

@@ -8,7 +8,6 @@ import (
 	"strings"
 	"time"
 
-	"github.com/Wei-Shaw/sub2api/internal/config"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/httpclient"
 	"github.com/Wei-Shaw/sub2api/internal/service"
 )
@@ -17,17 +16,12 @@ type pricingRemoteClient struct {
 	httpClient *http.Client
 }
 
-func NewPricingRemoteClient(cfg *config.Config) service.PricingRemoteClient {
-	allowPrivate := false
-	validateResolvedIP := true
-	if cfg != nil {
-		allowPrivate = cfg.Security.URLAllowlist.AllowPrivateHosts
-		validateResolvedIP = cfg.Security.URLAllowlist.Enabled
-	}
+// NewPricingRemoteClient 创建定价数据远程客户端
+// proxyURL 为空时直连，支持 http/https/socks5/socks5h 协议
+func NewPricingRemoteClient(proxyURL string) service.PricingRemoteClient {
 	sharedClient, err := httpclient.GetClient(httpclient.Options{
-		Timeout:            30 * time.Second,
-		ValidateResolvedIP: validateResolvedIP,
-		AllowPrivateHosts:  allowPrivate,
+		Timeout:  30 * time.Second,
+		ProxyURL: proxyURL,
 	})
 	if err != nil {
 		sharedClient = &http.Client{Timeout: 30 * time.Second}