feat(networking): add --disable-ipv6 flag for IPv4-only operation

[stevensbkang]

Introduces --disable-ipv6 (KUBESOLO_DISABLE_IPV6) to disable IPv6 across all layers when running on IPv4-only or constrained environments:

• OS: writes net.ipv6.conf.{all,default,lo}/disable_ipv6=1 via /proc/sys at bootstrap; idempotent — skips paths already set to 1
• CoreDNS: omits ip6.arpa reverse zone from the Corefile
• Kubelet: conditionally passes --node-ip to force IPv4-only node registration only when the flag is set, avoiding breakage on IPv6-only hosts

[linear]

KS-48

[Copilot]

Pull request overview

Adds an explicit IPv4-only operation mode by introducing a --disable-ipv6 / KUBESOLO_DISABLE_IPV6 switch and wiring it through bootstrap networking, CoreDNS configuration, and kubelet registration behavior.

Changes:

• Add --disable-ipv6 flag and persist it into types.Embedded.
• When enabled, disable IPv6 via /proc/sys/net/ipv6/conf/*/disable_ipv6 at bootstrap.
• When enabled, generate a CoreDNS Corefile without the ip6.arpa reverse zone and pass --node-ip to kubelet to force IPv4 node registration.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
types/types.go	Adds DisableIPv6 to the embedded runtime configuration struct.
internal/config/flags/flags.go	Introduces the --disable-ipv6 / KUBESOLO_DISABLE_IPV6 flag.
cmd/kubesolo/main.go	Plumbs the flag into bootstrap (sysctl write) and CoreDNS deploy parameters, and stores it in Embedded.
internal/runtime/network/ipv6.go	Implements the sysctl-based IPv6 disabling helper.
pkg/kubernetes/kubelet/service.go	Stores the new embedded DisableIPv6 setting in the kubelet service.
pkg/kubernetes/kubelet/args.go	Conditionally appends --node-ip when IPv6 is disabled.
pkg/components/coredns/coredns.go	Extends Deploy to accept the disableIPv6 option and forwards it to config creation.
pkg/components/coredns/configuration.go	Splits CoreDNS Corefile into IPv4-only vs dual-stack variants and selects based on flag.

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