feat(sub): auto-detect subscription format by User-Agent (Updated) (#5826)

* feat(settings): add subscription format controls

* feat(sub): auto-detect subscription formats

* fix(xray): validate balancer regexes before save

* Revert "fix(xray): validate balancer regexes before save"

This reverts commit 8a208ce71b.

* doc(endpoints): align indent spaces

* doc(settings): improve error message formatting in validateSubUserAgentRegex

- Use NewErrorf with proper formatting instead of NewError with string concatenation
- Add comment explaining the rationale for returning original pattern value
- This preserves the intentional design where empty input is stored as empty
  in the DB and inherited as the runtime default at read time

---------

Co-authored-by: Tomilla <5007859+Tomilla@users.noreply.github.com>
Co-authored-by: Sanaei <ho3ein.sanaei@gmail.com>

internal/web/controller/setting.go

@@ -2,6 +2,7 @@ package controller
 
 import (
 	"errors"
+	"net/http"
 	"strconv"
 	"time"
 
@@ -38,6 +39,10 @@ type updateSettingForm struct {
 	ClearSmtpPassword bool   `json:"clearSmtpPassword" form:"clearSmtpPassword"`
 }
 
+type validateRegexForm struct {
+	Regex string `json:"regex" form:"regex"`
+}
+
 // SettingController handles settings and user management operations.
 type SettingController struct {
 	settingService  service.SettingService
@@ -61,6 +66,7 @@ func (a *SettingController) initRouter(g *gin.RouterGroup) {
 	g.POST("/all", a.getAllSetting)
 	g.POST("/defaultSettings", a.getDefaultSettings)
 	g.POST("/update", a.updateSetting)
+	g.POST("/validateRegex", a.validateRegex)
 	g.POST("/updateUser", a.updateUser)
 	g.POST("/restartPanel", a.restartPanel)
 	g.GET("/getDefaultJsonConfig", a.getDefaultXrayConfig)
@@ -72,6 +78,19 @@ func (a *SettingController) initRouter(g *gin.RouterGroup) {
 	g.POST("/testTgBot", a.testTgBot)
 }
 
+func (a *SettingController) validateRegex(c *gin.Context) {
+	form := &validateRegexForm{}
+	if err := c.ShouldBind(form); err != nil {
+		pureJsonMsg(c, http.StatusOK, false, err.Error())
+		return
+	}
+	if err := service.ValidateRegex(form.Regex); err != nil {
+		pureJsonMsg(c, http.StatusOK, false, err.Error())
+		return
+	}
+	pureJsonMsg(c, http.StatusOK, true, "")
+}
+
 // getAllSetting retrieves all current settings as the browser-safe view:
 // secret values are redacted and surfaced as has* presence flags instead.
 func (a *SettingController) getAllSetting(c *gin.Context) {