feat(k8s/cluster): add security best practices documentation

[rafeegnash]

Summary

• Adds security warnings and recommendations for plan generation
• Provides helper functions to check security configurations
• Enables consistent security guidance across all cluster providers

Security Warnings

Key	Description
public-endpoint	Warns about public cluster endpoints
public-service	Warns about LoadBalancer services
no-network-policy	Suggests adding network policies
secrets-plain	Warns about plain Kubernetes secrets
root-container	Warns about running as root
privileged	Warns about privileged containers
host-network	Warns about host network usage
no-resource-limits	Suggests adding resource limits

Security Recommendations

Recommendations available for scenarios:

• new-cluster
• new-deployment
• new-service
• secrets

Helper Functions

Function	Description
GetSecurityWarning	Returns warning for a given key
GetSecurityRecommendations	Returns recommendations for a scenario
IsPublicEndpoint	Checks if cluster has public-only endpoint
ShouldWarnPublicAccess	Checks if public access warning should be shown

Test Plan

• Build passes
• All cluster tests pass
• Security function tests pass (30 test cases)

Closes bgdnvk#76