feat(sub): allow identity tokens on every subscription link (#5935)

Keep usage tokens first-link-only while adding an opt-in setting for repeating EMAIL and USERNAME in subscription-body remarks.

Co-authored-by: x06579 <x06579@ai-dashboard>

internal/web/service/setting_sub_identity_test.go

@@ -0,0 +1,39 @@
+package service
+
+import "testing"
+
+func TestSubShowIdentityOnAllLinksDefaultsAndPersists(t *testing.T) {
+	setupSettingTestDB(t)
+	s := &SettingService{}
+
+	if got, err := s.GetSubShowIdentityOnAllLinks(); err != nil || got {
+		t.Fatalf("missing setting = %t, %v; want false, nil", got, err)
+	}
+	settings, err := s.GetAllSetting()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if settings.SubShowIdentityOnAllLinks {
+		t.Fatal("GetAllSetting returned true for a missing setting")
+	}
+
+	settings.SubShowIdentityOnAllLinks = true
+	if err := s.UpdateAllSetting(settings, SecretClears{}); err != nil {
+		t.Fatal(err)
+	}
+	if got, err := s.GetSubShowIdentityOnAllLinks(); err != nil || !got {
+		t.Fatalf("persisted setting = %t, %v; want true, nil", got, err)
+	}
+
+	settings, err = s.GetAllSetting()
+	if err != nil {
+		t.Fatal(err)
+	}
+	settings.SubShowIdentityOnAllLinks = false
+	if err := s.UpdateAllSetting(settings, SecretClears{}); err != nil {
+		t.Fatal(err)
+	}
+	if got, err := s.GetSubShowIdentityOnAllLinks(); err != nil || got {
+		t.Fatalf("persisted setting = %t, %v; want false, nil", got, err)
+	}
+}