docs: add portable LLM workflow skill

docs/llm-workflow-runbooks.md

@@ -12,6 +12,12 @@ behavior they rely on already exists (canonical runtime profiles, the
 interactive setup menu, identity/eligibility checks, gated review/merge, and
 audit logging). See [Related documents](#related-documents).
 
+For cross-project use, copy the portable workflow skill at
+[`../skills/llm-project-workflow/SKILL.md`](../skills/llm-project-workflow/SKILL.md).
+It extracts the issue-first, isolated-worktree, no-self-review, profile-safety,
+merge-cleanup, fail-closed, and recovery rules into a reusable package that can
+be adapted to other repositories.
+
 ## Principle: the profile is the role, not the LLM
 
 ```text
@@ -316,6 +322,7 @@ with the profile and authenticated user when `GITEA_AUDIT_LOG` is set (see
 
 ## Related documents
 
+- [`../skills/llm-project-workflow/SKILL.md`](../skills/llm-project-workflow/SKILL.md) — portable cross-project LLM workflow skill.
 - [`gitea-execution-profiles.md`](gitea-execution-profiles.md) — the profile model.
 - [`safety-model.md`](safety-model.md) — trust boundaries and audit logging.
 - [`tool-boundaries.md`](tool-boundaries.md) — per-tool allowed operations.