Let TerdutServer customize its pod, and never manage its own ingress

spec.pod (api/v1alpha1/terdutserver_types.go): annotations, nodeSelector,
tolerations, affinity, topologySpreadConstraints, resources, pod and
container securityContext, serviceAccountName, extraEnv/extraEnvFrom,
extraVolumes/extraVolumeMounts, imagePullSecrets, and an optional
disruptionBudget. All direct corev1 passthrough -- no wrapper types buy
anything for any of these, matching how CloudNativePG and the Zalando
postgres-operator both expose the same knobs, and matching this repo's
own SweeperSpec precedent ("wrap only when a round-trip through a
different type buys something"). affinity is pure user-supplied
passthrough, not a toggle-plus-generated-default the way a multi-replica
cluster operator's pod anti-affinity usually is: this operator never
auto-generates one, since spec.replicas above 1 isn't a supported
topology (the sweeper/notifier singleton constraint). Considered and
declined for this round: priorityClassName, pod labels beyond
annotations, and a HorizontalPodAutoscaler -- the last of those would
directly contradict the singleton constraint above.

disruptionBudget is the one field here that isn't a plain PodTemplateSpec
knob: when set, the controller now reconciles a PodDisruptionBudget
selecting the TerdutServer's own pods (new terdutserver_pdb.go); clearing
it deletes any it previously created. New RBAC marker on
poddisruptionbudgets to match.

Driven by a public-release pass: looking past this project's own use case
at what a mature, general-purpose operator CRD exposes here (researched
against Zalando postgres-operator and CloudNativePG specifically), not
just the fields this install happened to need.

Separately, and found while answering a question about exposing
TerdutServer through Istio instead of Gateway API: spec.networking's own
doc comment quietly promised a Gateway API HTTPRoute this operator would
build eventually ("a near-term follow-up, not deferred"). That promise is
wrong for a public release -- an operator managing someone's ingress
mechanism for them is a worse default than not touching it at all, and a
surprise HTTPRoute appearing once that follow-up eventually landed would
have been exactly backwards for an Istio (or plain-Ingress, or
intentionally-unexposed) install. Made the non-goal explicit and
permanent instead (DESIGN.md §1), removed the dead `gatewayListener`
field it was the only consumer of (zero runtime call sites anywhere --
setting it already had no effect, so this is a schema cleanup, not a
behavior change), and corrected ROADMAP.md's framing. hostname/servicePort
stay: both are live (TERDUT_PUBLIC_URL, container/Service port), this
operator just never acts on hostname for exposure. Added
examples/networking (Gateway API HTTPRoute, Istio VirtualService) showing
how to expose the plain ClusterIP Service the operator already creates --
outside the operator itself, as illustrations, not as something
examples/demo applies automatically.

No new terdut-server version requirement: both changes are CRD/controller-
only, nothing about the API this operator's bootstrap flow depends on
changed.

internal/controller/terdutserver_controller.go

@@ -8,6 +8,7 @@ import (
 
 	appsv1 "k8s.io/api/apps/v1"
 	corev1 "k8s.io/api/core/v1"
+	policyv1 "k8s.io/api/policy/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/api/meta"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
@@ -97,6 +98,7 @@ type TerdutServerReconciler struct {
 // +kubebuilder:rbac:groups="",resources=secrets,verbs=get;list;watch;create;update;patch;delete
 // +kubebuilder:rbac:groups="",resources=services,verbs=get;list;watch;create;update;patch;delete
 // +kubebuilder:rbac:groups=apps,resources=deployments,verbs=get;list;watch;create;update;patch;delete
+// +kubebuilder:rbac:groups=policy,resources=poddisruptionbudgets,verbs=get;list;watch;create;update;patch;delete
 // +kubebuilder:rbac:groups=acid.zalan.do,resources=postgresqls,verbs=get;list;watch
 // +kubebuilder:rbac:groups=events.k8s.io,resources=events,verbs=create;patch
 
@@ -137,6 +139,9 @@ func (r *TerdutServerReconciler) Reconcile(ctx context.Context, req ctrl.Request
 	if err := r.reconcileService(ctx, &srv); err != nil {
 		return ctrl.Result{}, err
 	}
+	if err := r.reconcilePodDisruptionBudget(ctx, &srv); err != nil {
+		return ctrl.Result{}, err
+	}
 
 	meta.SetStatusCondition(&srv.Status.Conditions, metav1.Condition{
 		Type:    terdutv1alpha1.ConditionDatabaseReady,
@@ -246,6 +251,7 @@ func (r *TerdutServerReconciler) SetupWithManager(mgr ctrl.Manager) error {
 		For(&terdutv1alpha1.TerdutServer{}).
 		Owns(&appsv1.Deployment{}).
 		Owns(&corev1.Service{}).
+		Owns(&policyv1.PodDisruptionBudget{}).
 		Named("terdutserver").
 		Complete(r)
 }