refactor: remove HostnamePolicyNone enum value, use nil for "no policy"

The combination of pointer + optional + sentinel value "None" created
three states (nil, None, PodName) where only two are meaningful, which
is error-prone (comparing *hp == HostnamePolicyNone vs hp == nil).
Drop the None enum value and treat nil/empty as "no policy", consistent
with CollaSetSpec convention (e.g. NamingStrategy uses pointer-or-nil
for "unset").

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ColdsteelRail

apps/v1alpha1/collaset_types.go

@@ -57,12 +57,10 @@ const (
 )
 
 // HostnamePolicyType indicates how the pod's hostname is determined.
-// +kubebuilder:validation:Enum=None;PodName
+// +kubebuilder:validation:Enum=PodName
 type HostnamePolicyType string
 
 const (
-	// HostnamePolicyNone means no hostname policy is applied.
-	HostnamePolicyNone HostnamePolicyType = "None"
 	// HostnamePolicyPodName sets the pod's hostname to the pod name.
 	// This requires namingStrategy.podNamingSuffixPolicy to be PersistentSequence,
 	// as the pod name must be deterministic before creation.
@@ -140,6 +138,7 @@ type CollaSetSpec struct {
 	NamingStrategy *NamingStrategy `json:"namingStrategy,omitempty"`
 
 	// HostnamePolicy indicates how the pod's hostname is determined.
+	// When unset (nil), no hostname policy is applied.
 	// When set to "PodName", the pod's spec.hostname will be set to the pod name.
 	// This requires NamingStrategy.PodNamingSuffixPolicy to be PersistentSequence.
 	// +optional

config/crd/apps/apps.kusionstack.io_collasets.yaml

@@ -86,10 +86,10 @@ spec:
               hostnamePolicy:
                 description: |-
                   HostnamePolicy indicates how the pod's hostname is determined.
+                  When unset (nil), no hostname policy is applied.
                   When set to "PodName", the pod's spec.hostname will be set to the pod name.
                   This requires NamingStrategy.PodNamingSuffixPolicy to be PersistentSequence.
                 enum:
-                - None
                 - PodName
                 type: string
               namingStrategy: