docs: update k3s setup command for metrics-server fix [doc-updater]

[james-in-a-box]

Update documentation to reflect changes from 129033c (Fix fresh-cluster local k3s bring-up: Cilium datapath + namespace ordering, #2705):

• Updated the k3s install command example in docs/guides/deployment.md to include --disable=metrics-server and --write-kubeconfig-mode=644, matching the actual make k3s-setup command.
• Added a "Why --disable=metrics-server?" callout explaining that under Cilium, the metrics-server pod cannot reach the kubelet node IP and never becomes Ready; the resulting unavailable APIService wedges all namespace deletion. egg doesn't use metrics-server, so disabling it prevents hung Terminating namespaces during test teardown and CI cleanup.

Triggered by: #2705

Authored-by: egg

[egg-reviewer]

Review

Verified the diff against Makefile:487 and the explanatory comment at Makefile:476-484. The doc update is accurate and consistent:

• The INSTALL_K3S_EXEC flag string in docs/guides/deployment.md:62 now matches the Makefile command byte-for-byte.
• The new "Why --disable=metrics-server?" callout faithfully restates the rationale already captured in the Makefile comment and the #2705 PR body (metrics-server pod can't reach the kubelet under Cilium → APIService perpetually unavailable → namespace controller discovery fails → namespaces stuck Terminating).
• Grep confirms no stale references to the old command elsewhere in docs/.

No blocking issues.

Non-blocking

• --write-kubeconfig-mode=644 is now visible in the example command but isn't explained anywhere in the guide. It is self-explanatory to anyone who has read chmod(1), and #2705 didn't actually add it (it's been on the target for a while — this PR is just surfacing it in the docs), so there's no obligation to backfill an explanation here. Worth a one-line callout someday if the deployment guide grows a more complete "k3s install flags" section, but not in this PR.

— Authored by egg

[james-in-a-box]

egg is addressing review feedback...

[james-in-a-box]

Review Response

Item 1: Non-blocking — explain --write-kubeconfig-mode=644 in the guide

• Disposition: disagree (reviewer explicitly stated "no obligation to backfill an explanation here" and "not in this PR"; flag is self-explanatory from chmod(1) and predates #2705)

The reviewer's own framing — "not in this PR," "no obligation," "worth a one-line callout someday if the deployment guide grows a more complete 'k3s install flags' section" — indicates this is a future-scope observation, not a request for this PR. Leaving as-is. If a broader "k3s install flags" section is later added to the deployment guide, a one-line note on the kubeconfig mode would fit naturally there.

— Authored by egg

[james-in-a-box]

egg feedback addressed. View run logs

1 previous review(s) hidden.