refactor(cluster): rename check_manifest_usage to kebab-case

What

glab cluster agent check_manifest_usage is the only snake_case command name in the CLI. Every sibling under the same noun is kebab-case:

Command	Name
cluster agent get-token	kebab
cluster agent update-kubeconfig	kebab
cluster agent token-cache	kebab
cluster agent check_manifest_usage	snake

The snake_case Go package directory (internal/commands/cluster/agent/check_manifest_usage/) is conventional here — get_token/, update_kubeconfig/ and token_cache/ do the same — so only the user-facing Use string changes.

Usage evidence

This came out of an audit of the full gitlab_cli_command_used export (196 rows × 442 days, 15/05/2025 → 20/08/2026), where it was the only naming outlier. It is also close to unused:

Command	Events	Days active	Last event
cluster agent get-token	4,911	403	20/08/2026
cluster agent list	968	170	17/08/2026
cluster agent update-kubeconfig	556	268	19/08/2026
cluster agent bootstrap	376	148	14/08/2026
cluster agent check_manifest_usage	1	1	29/01/2026

One invocation in fourteen months, against 4,911 for get-token in the same noun. The command is also marked (EXPERIMENTAL), so it carries no stability guarantee. The blast radius of the rename is as close to zero as the data can show.

Backward compatibility

The original name is kept as a cobra alias:

Use: "check-manifest-usage [flags]",
// Retain the original snake_case name so existing invocations keep working.
Aliases: []string{"check_manifest_usage"},

Aliases do not appear in help output, so glab cluster agent --help lists only check-manifest-usage, while the old form keeps working for anyone scripting it. Cobra reports the canonical name in CommandPath(), so telemetry records the kebab-case form from now on.

Given the usage above and the EXPERIMENTAL marker, dropping the alias entirely is also defensible — happy to remove it if reviewers prefer a clean break.

Verification

$ glab cluster agent check_manifest_usage --help   # old name still resolves
$ glab cluster agent check-manifest-usage --help   # new name resolves
$ glab cluster agent --help | grep manifest
    check-manifest-usage [--flags]   Find agents using deprecated GitOps manifest settings. (EXPERIMENTAL)

Docs regenerated with make gen-docs: the page moves to check-manifest-usage.md, and _index.md plus navigation-glab.yaml update automatically. Pre-push hooks pass (build, lint, tests, generated-doc check).