fix(config): serve public settings and enforce login CAP

Public config now comes from admin as a flat visibility=1 map instead of
a cross-plugin query that compared an integer column to "visible". Login
and register resolve CaptchaService per request so CAP is not skipped
when user applies before cap.

backend/plugins/domain/admin/plugin.go

@@ -92,6 +92,7 @@ func (p *Plugin) Apply(ctx *core.Context) error {
 	core.Bind[contracts.StorageService](ctx, service.SetStorageService)
 	core.Bind[contracts.RiskControlService](ctx, service.SetRiskControlService)
 	service.SetEventEmitter(ctx.Events().Emit)
+	core.Provide[contracts.PublicConfigProvider](ctx, service.PublicConfigAdapter{})
 
 	ctx.OnDispose(func() error {
 		service.ResetServices()