#6: Align living-doc with the fleet's CI conventions

[miroslavpojer]

Overview

Closes out Phase 0 residual P0-R3: living-doc was the last repo in the ecosystem still missing
link-check.yml and still using the non-canonical gh_release_draft.yml filename. This PR:

• Adds .github/workflows/link-check.yml, copied from living-doc-collector-gh's reference copy
  (detect + noop shape, lychee link check over tracked Markdown — docs/specs/** is git-ignored
  here so it's out of scope for the check, same as every other doc directory that isn't tracked).
• Renames .github/workflows/gh_release_draft.yml → release_draft.yml and updates its name:
  field from GitHub Draft Release to Draft Release, matching every other repo in the fleet
  (collector-gh, collector-ad, toolkit, generator-pdf). No trigger, input, or job logic
  changed — same workflow_dispatch inputs, same steps.

With this merged, all five Phase 0 residuals (P0-R1–P0-R5) are closed and Phase 0 is done.

Release Notes

• Added link-check.yml to validate Markdown links on doc changes.
• Renamed the release-draft workflow file to release_draft.yml (no functional change).

Related

Closes #6