ci: inline doc lint workflow, drop vyos/.github cross-repo dependency

The reusable lint-doc workflow at vyos/.github checks out vyos/.github
on the consumer's PR base.ref to source doc-linter.py — designed for
per-release-train linter rules. With this repo's default renamed
current → rolling and vyos/.github still on current, the checkout
errors with "fetch +refs/heads/rolling*: exit code 1".

Rather than chase branch parity across repos, move the linter where it
belongs: doc-linter.py is doc-specific and only consumed here. Inlining
removes the cross-repo coupling permanently and unblocks any future
branch renames in this repo without touching vyos/.github.

- scripts/doc-linter.py: copied byte-for-byte from
  vyos/.github@current:.github/doc-linter.py (sha
  3dc7c2fc16242e62b0ea7107f767577e999ca417 — identical across all four
  release-train branches in vyos/.github, so no behavioral change).
- .github/workflows/lint-doc.yml: replaces `uses:
  vyos/.github/.github/workflows/lint-doc.yml@current` with the inlined
  steps. Same actions (bullfrogsec/bullfrog, trilom/file-changes-action,
  setup-python) and the same final invocation, just sourcing the script
  from this repo. Adds explicit minimal permissions (contents/pull-requests
  read) and passes the file list via env var to follow the workflow-
  injection guidance.

Follow-up: vyos/.github still hosts the now-orphaned doc-linter.py and
its reusable workflow — separate cleanup PR can delete them once any
other consumers migrate (none observed today; this repo was the only
caller).

🤖 Generated by [robots](https://vyos.io)

0 files changed, 0 insertions, 0 deletions