fix(inbounds): allow negative subSortIndex for subscription order (#6465)

* fix(inbounds): allow negative subSortIndex for subscription order

Preserve explicitly set negative indices so primary inbounds can sort
ahead of the default without renumbering peers; keep 0/omitted → 1.

* fix(inbounds): gofumpt model.go and trim subSortIndex comments

---------

Co-authored-by: mrchatam <287639636+mrchatam@users.noreply.github.com>

internal/web/service/inbound_util_test.go

@@ -0,0 +1,20 @@
+package service
+
+import "testing"
+
+func TestNormalizeSubSortIndex(t *testing.T) {
+	cases := []struct {
+		in, want int
+	}{
+		{0, 1},
+		{1, 1},
+		{7, 7},
+		{-1, -1},
+		{-10, -10},
+	}
+	for _, tc := range cases {
+		if got := normalizeSubSortIndex(tc.in); got != tc.want {
+			t.Fatalf("normalizeSubSortIndex(%d) = %d, want %d", tc.in, got, tc.want)
+		}
+	}
+}