feat(vks): flag revamp (enabled/disabled toggles, TIGERA, os rocky) + drop get-nodegroup-events

[vks-team]

Summary

1. Remove get-nodegroup-events command (file, registration, docs, nav, README).
2. network-type: CALICO → TIGERA in --help, completion, and the --cidr-required validation (API accepts TIGERA, not CALICO).
3. --os: add rocky → ubuntu, linux, rocky (default ubuntu).
4. Toggle flags → <enabled|disabled> (via a shared parseToggle helper that rejects invalid values):
   • create-cluster: --private-cluster (default disabled), --private-nodes (disabled), --load-balancer-plugin (enabled), --block-store-csi-plugin (enabled)
   • create-nodegroup: --private-nodes (disabled)
   • update-cluster: --load-balancer-plugin / --block-store-csi-plugin (unset = unchanged) — replaces the old --enabled-*/--no-* pairs

(Task "get-versions" dropped — list-cluster-versions already covers it.)

⚠️ Breaking

Old flags removed: --enable-private-cluster, --enable-private-nodes, --no-load-balancer-plugin, --no-block-store-csi-plugin (create-cluster); --enable-private-nodes (create-nodegroup); --enabled-*/--no-* plugin flags (update-cluster). CALICO no longer accepted for --network-type. get-nodegroup-events removed.

Test plan

• build / vet / go test ./... pass
• --help shows new flags + defaults; get-nodegroup-events gone
• invalid toggle value rejected (--private-cluster bogus → clear error)
• completion: --os → ubuntu/linux/rocky; --network-type → TIGERA/...; toggles → enabled/disabled
• smoke-test create-cluster/create-nodegroup against a live project

🤖 Generated with Claude Code

[vks-team]

Added a bonus bugfix in e10fb6f: grn configure --profile <name> no longer panics for a profile that doesn't exist yet.

Root cause: config.LoadConfig returns (nil, err) when the profile is absent from the credentials file, but runConfigure ignored the error and dereferenced nil at configure.go:47 (the crash you hit on --profile prod-han-qc2). Now it guards for err/nil and starts from empty defaults so the profile can be created.

Verified: grn configure --profile <new> prompts and saves without crashing; full test suite passes.