[workflow-editor] docs-linker: trim redundant prompt sections

[Copilot]

The docs-linker workflow brief repeated docs-site and URL-validation context that was already established in Load State. This change removes that duplicated guidance and keeps the prompt focused on the validated doc index as the single source of truth.

• Prompt cleanup

  • Removed the standalone ## Docs site section from .github/workflows/docs-linker.md.
  • Kept the workflow brief centered on the prevalidated index loaded in ## Load State.

• Validation guidance dedup

  • Reduced ## Verify Concept Coverage to the decision rules that affect agent behavior.
  • Preserved the only actionable guardrail: discard any doc_url not present in the validated index.

• Compiled workflow sync

  • Regenerated .github/workflows/docs-linker.lock.yml so the compiled workflow matches the edited source brief.

Example of the retained rule shape:

## Verify Concept Coverage (Doc Index Check)

- If the matched entry came from a **section anchor**, its `text` field must
  contain at least one word from the identified concept term.
- If the matched entry is a **page-level URL** (no anchor), the page title must
  be topically related to the concept.
- Discard any `doc_url` that does not appear in the validated index.

• Fixes [workflow-editor] docs-linker: remove redundant Docs site section and validation reminders #1890