feat: 添加IP竞速拨号器与IP偏好设置，连接状态显示域名与实际IP

- 新增竞速拨号器(racedial.go)：域名连接时并行解析所有A/AAAA记录，
  同时对所有IP发起TCP连接，第一个成功的胜出，确保选择延迟最低的地址
- ServerProfile新增IPPreference字段(auto/v4/v6)，支持用户指定IP版本偏好
- 填写服务器IP时跳过域名解析直接使用IP，顺序failover
- 连接成功后状态栏显示「已连接 (域名 -> 实际IP)」
- DB迁移v6：server_profiles表添加ip_preference列
- WebSocket拨号与HTTP登录均使用竞速拨号器
- 补充中英文i18n翻译

internal/transport/racedial.go

@@ -0,0 +1,135 @@
+package transport
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"time"
+)
+
+// NewRaceDialer returns a dial function suitable for use as a
+// websocket.Dialer.NetDialContext or http.Transport.DialContext.
+//
+// When the host in addr is a domain name, it resolves all A/AAAA
+// records and dials them concurrently, returning the first successful
+// connection (true parallel racing, not Happy Eyeballs staggered start).
+//
+// preference controls which address families participate:
+//   - "auto": race all resolved addresses (v4 + v6)
+//   - "v4":   only IPv4 addresses
+//   - "v6":   only IPv6 addresses
+//
+// When the host is an IP literal (CDN failover or direct IP mode), it
+// dials directly without racing — there is only one target.
+func NewRaceDialer(preference string) func(ctx context.Context, network, addr string) (net.Conn, error) {
+	return func(ctx context.Context, network, addr string) (net.Conn, error) {
+		host, port, err := net.SplitHostPort(addr)
+		if err != nil {
+			return nil, fmt.Errorf("split host port: %w", err)
+		}
+
+		// IP literal: dial directly, no racing.
+		if ip := net.ParseIP(host); ip != nil {
+			d := &net.Dialer{}
+			return d.DialContext(ctx, network, addr)
+		}
+
+		// Domain name: resolve and race.
+		ips, err := resolveAndFilter(ctx, host, preference)
+		if err != nil {
+			return nil, err
+		}
+
+		if len(ips) == 1 {
+			d := &net.Dialer{}
+			return d.DialContext(ctx, network, net.JoinHostPort(ips[0], port))
+		}
+
+		return raceDial(ctx, network, ips, port)
+	}
+}
+
+// resolveAndFilter resolves a hostname and filters by preference.
+func resolveAndFilter(ctx context.Context, host, preference string) ([]string, error) {
+	resolveCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+
+	addrs, err := net.DefaultResolver.LookupIPAddr(resolveCtx, host)
+	if err != nil {
+		return nil, fmt.Errorf("lookup %s: %w", host, err)
+	}
+
+	var ips []string
+	for _, a := range addrs {
+		isV4 := a.IP.To4() != nil
+		switch preference {
+		case "v4":
+			if isV4 {
+				ips = append(ips, a.IP.String())
+			}
+		case "v6":
+			if !isV4 {
+				ips = append(ips, a.IP.String())
+			}
+		default: // "auto" or unspecified
+			ips = append(ips, a.IP.String())
+		}
+	}
+
+	if len(ips) == 0 {
+		return nil, fmt.Errorf("lookup %s: no addresses for preference %q", host, preference)
+	}
+	return ips, nil
+}
+
+// raceDial dials all IPs concurrently and returns the first successful
+// connection. Losing connections are closed and their errors discarded.
+func raceDial(ctx context.Context, network string, ips []string, port string) (net.Conn, error) {
+	type result struct {
+		conn net.Conn
+		err  error
+	}
+
+	raceCtx, cancel := context.WithCancel(ctx)
+	defer cancel()
+
+	resultCh := make(chan result, len(ips))
+
+	for _, ip := range ips {
+		go func(target string) {
+			d := &net.Dialer{}
+			c, err := d.DialContext(raceCtx, network, net.JoinHostPort(target, port))
+			select {
+			case resultCh <- result{conn: c, err: err}:
+			case <-raceCtx.Done():
+				if c != nil {
+					c.Close()
+				}
+			}
+		}(ip)
+	}
+
+	var firstErr error
+	for i := 0; i < len(ips); i++ {
+		r := <-resultCh
+		if r.err == nil {
+			// Winner. Cancel remaining dialers; drain and close
+			// any late successful connections.
+			cancel()
+			for j := i + 1; j < len(ips); j++ {
+				if late := <-resultCh; late.conn != nil {
+					late.conn.Close()
+				}
+			}
+			return r.conn, nil
+		}
+		if firstErr == nil {
+			firstErr = r.err
+		}
+	}
+
+	if firstErr == nil {
+		firstErr = fmt.Errorf("all dial attempts failed")
+	}
+	return nil, firstErr
+}