fix: 修复 Windows 端 IPv6 无法下行的问题

根因: netsh interface ipv6 命令参数名用错
- configureIPv6Addr: name= → interface=,IPv6 地址未实际分配到适配器
- SetMTU IPv6: name= → interface=

路由修复:
- cidrToV6Prefix: 用 Mask.Size() 取前缀长度,修复 fmt.Sprintf(%d, mask) 输出字节切片的 bug
- addRoute6/deleteRoute6: netsh → route -6,用 :: 作 on-link gateway
- addRouteVia6/deleteRouteVia6: 加 -6 flag
- defaultGateway6: route -6 print :: → route -6 print(避免过滤掉 ::/0)
- applyFull: IPv6 bypass 路由失败不再阻断全隧道路由

internal/route/route.go

@@ -138,12 +138,14 @@ func (m *Manager) applyFull() error {
 	}
 
 	// Bypass: server's public IPv6 via the original v6 gateway.
+	// Non-fatal: if this fails, full-tunnel routes are still added.
 	if v6 != "" && gw6 != "" {
 		bypassSpec := v6 + "/128"
 		if err := addRouteVia6(bypassSpec, gw6); err != nil {
-			return fmt.Errorf("add server bypass6 route: %w", err)
+			m.serverBypass6 = false
+		} else {
+			m.serverBypass6 = true
 		}
-		m.serverBypass6 = true
 	}
 
 	// Two /1 routes cover the entire IPv4 space and are more specific

internal/route/route_windows.go

@@ -75,7 +75,8 @@ func cidrToV6Prefix(cidr string) (network, prefix string, err error) {
 	if err != nil {
 		return "", "", err
 	}
-	return ipNet.IP.String(), fmt.Sprintf("%d", ipNet.Mask), nil
+	ones, _ := ipNet.Mask.Size()
+	return ipNet.IP.String(), fmt.Sprintf("%d", ones), nil
 }
 
 func addRoute6(cidr, iface string) error {
@@ -87,8 +88,8 @@ func addRoute6(cidr, iface string) error {
 	if err != nil {
 		return err
 	}
-	return runCmd("netsh", "interface", "ipv6", "add", "route",
-		network+"/"+prefix, "interface="+fmt.Sprintf("%d", idx), "metric=1")
+	return runCmd("route", "-6", "add", network+"/"+prefix, "::",
+		"if", fmt.Sprintf("%d", idx), "metric", "1")
 }
 
 func deleteRoute6(cidr, iface string) error {
@@ -96,12 +97,7 @@ func deleteRoute6(cidr, iface string) error {
 	if err != nil {
 		return err
 	}
-	idx, err := ifaceIndex(iface)
-	if err != nil {
-		return err
-	}
-	return runCmd("netsh", "interface", "ipv6", "delete", "route",
-		network+"/"+prefix, "interface="+fmt.Sprintf("%d", idx))
+	return runCmd("route", "-6", "delete", network+"/"+prefix, "::")
 }
 
 func addRouteVia6(cidr, gateway string) error {
@@ -109,8 +105,7 @@ func addRouteVia6(cidr, gateway string) error {
 	if err != nil {
 		return err
 	}
-	return runCmd("netsh", "interface", "ipv6", "add", "route",
-		network+"/"+prefix, gateway, "metric=1")
+	return runCmd("route", "-6", "add", network+"/"+prefix, gateway, "metric", "1")
 }
 
 func deleteRouteVia6(cidr, gateway string) error {
@@ -118,8 +113,7 @@ func deleteRouteVia6(cidr, gateway string) error {
 	if err != nil {
 		return err
 	}
-	return runCmd("netsh", "interface", "ipv6", "delete", "route",
-		network+"/"+prefix, gateway)
+	return runCmd("route", "-6", "delete", network+"/"+prefix, gateway)
 }
 
 // --- Default gateway ---
@@ -133,7 +127,7 @@ func defaultGateway() (string, error) {
 }
 
 func defaultGateway6() (string, error) {
-	out, err := exec.Command("route", "-6", "print", "::").Output()
+	out, err := exec.Command("route", "-6", "print").Output()
 	if err != nil {
 		return "", err
 	}

internal/tun/tun_windows.go

@@ -116,12 +116,16 @@ func (d *wintunDevice) ConfigureIPv6(localIP6 net.IP, prefix6 int) error {
 func (d *wintunDevice) configureIPv6Addr(ip net.IP, prefix int) error {
 	addr := fmt.Sprintf("%s/%d", ip.String(), prefix)
 	return execCmd("netsh", "interface", "ipv6", "add", "address",
-		"name="+d.name, "address="+addr)
+		"interface="+d.name, "address="+addr)
 }
 
 func (d *wintunDevice) SetMTU(mtu int) error {
-	return execCmd("netsh", "interface", "ipv4", "set", "subinterface",
-		"name="+d.name, fmt.Sprintf("mtu=%d", mtu))
+	if err := execCmd("netsh", "interface", "ipv4", "set", "subinterface",
+		"name="+d.name, fmt.Sprintf("mtu=%d", mtu)); err != nil {
+		return err
+	}
+	return execCmd("netsh", "interface", "ipv6", "set", "subinterface",
+		"interface="+d.name, fmt.Sprintf("mtu=%d", mtu))
 }
 
 // ensureWintunDLL extracts the embedded wintun.dll to the executable's