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/host_sub_test.go

@@ -304,7 +304,7 @@ func TestSub_HostSockoptJSON(t *testing.T) {
 		SockoptParams: `{"tcpFastOpen":true}`,
 	})
 	js := NewSubJsonService("", "", "", NewSubService(""))
-	out, _, err := js.GetJson("s1", "req.example.com")
+	out, _, err := js.GetJson("s1", "req.example.com", false)
 	if err != nil {
 		t.Fatalf("GetJson: %v", err)
 	}
@@ -322,7 +322,7 @@ func TestSub_HostMuxJSON(t *testing.T) {
 		MuxParams: `{"enabled":true,"concurrency":8}`,
 	})
 	js := NewSubJsonService("", "", "", NewSubService(""))
-	out, _, err := js.GetJson("s1", "req.example.com")
+	out, _, err := js.GetJson("s1", "req.example.com", false)
 	if err != nil {
 		t.Fatalf("GetJson: %v", err)
 	}