fix(cloud): repoint 8 dead cloud.google.com doc links

[pucedoteth]

Nine link occurrences across six skills return 404 on Google's current docs host. They sit in the "External Resources" / "Resources" sections these skills point an agent at, so an agent following them lands on a 404.

dead path	replacement
kubernetes-engine/docs/how-to/rollout-sequencing	kubernetes-engine/docs/concepts/about-rollout-sequencing
load-balancing/docs/overview	load-balancing/docs/load-balancing-overview
kubernetes-engine/docs/how-to/secret-manager ×2	secret-manager/docs/secret-manager-managed-csi-component
binary-authorization/docs/getting-started-gke	binary-authorization/docs/setting-up
kubernetes-engine/docs/concepts/sandbox	kubernetes-engine/docs/concepts/sandbox-pods
kubernetes-engine/docs/how-to/pod-security-standards	kubernetes-engine/docs/how-to/podsecurityadmission
bigtable/docs/reference/sql	bigtable/docs/googlesql-overview
alloydb/docs/reference/	alloydb/docs/reference/rest

Each replacement was checked for a 200 and for a page title matching the existing link text — e.g. secret-manager-managed-csi-component renders as "Use Secret Manager add-on with Google Kubernetes Engine", which covers both the "Secret Manager Add-on for GKE" and "Google Secret Manager CSI Driver" link texts, and binary-authorization/docs/setting-up renders as "Set up for GKE". After the change all 89 cloud.google.com links under skills/ resolve.

Only link targets changed; no link text, prose, or code was touched.

Two notes:

• I swept all 837 external URLs under skills/ and plugins/. The only other failures were ~15 registry.terraform.io URLs, which are not broken — that host returns "Content not available in your region" for every path from my location, including its own root. I left those alone.
• I see CONTRIBUTING says external PRs aren't accepted. Happy to close this and refile as an issue if you prefer — the table above is the whole report, so nothing is lost either way.

Unrelated finding

skills/cloud/agent-platform-alert-configuration/scripts/analyze_traffic_test.py fails for anyone outside Google: it reads mock data from agent-platform-alert-configuration/_internal, which is not in the repo, not gitignored, and not a submodule, so all 12 of its cases error with FileNotFoundError. The other 13 Python test files pass. I did not touch it because the fix could be either publishing the fixtures or dropping the test, which is your call — happy to file it separately.

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