[JakeSCahill]

Adds a link-check job to test.yml that runs on pull requests. It calls the reusable pr-link-check.yml from docs-extensions-and-macros, which checks the external URLs a PR adds in non-test Go files. 404 and 410 get a warning annotation at the file and line, and other failures are listed as couldn't check in the job summary. It never fails the PR, needs no secrets, and only has contents: read and pull-requests: read.

This catches dead doc-string links on the PR instead of in the weekly docs-site link check after merge (redpanda-data/docs-site#291).

The workflow is pinned to a commit on redpanda-data/docs-extensions-and-macros#440. Once that PR merges, re-pin to the merge or release SHA, the same way connect pins connect-docs-check.yml.

Dry run of the script on #510's diff: it finds the two added w3.org multipart URLs in output_http_client.go and processor_http.go (w3.org answers 403, so they're listed as couldn't check). On #524 it finds none, since every added URL there is in a test file or a comment.

[claude]

Commits
LGTM

Review
Adds an advisory link-check job to .github/workflows/test.yml. It calls the reusable pr-link-check.yml workflow from redpanda-data/docs-extensions-and-macros, pinned to a commit SHA. The job only runs on pull_request events and has read-only permissions (contents: read, pull-requests: read). No issues found.

LGTM