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/sub/sub_scale_test.go

@@ -212,7 +212,7 @@ func TestGetSubsScale(t *testing.T) {
 			jsonSvc := NewSubJsonService("", "", "", &SubService{})
 			start = time.Now()
 			for range reps {
-				body, _, err := jsonSvc.GetJson(scaleTargetSubId, "sub.example.com")
+				body, _, err := jsonSvc.GetJson(scaleTargetSubId, "sub.example.com", false)
 				if err != nil {
 					t.Fatalf("GetJson: %v", err)
 				}