docs: add release/version process SOP (#68)

Add docs/release-version-sop.md: operator SOP for cutting a versioned
release — master-based flow, SemVer bump decision, version-bump PR prep,
required pre-release checks, scripts/release-tag policy (safe-by-default,
master-only, clean-tree, tag-after-merge), who may merge/tag, self-review/
self-merge restrictions, status:in-progress handling, worktree cleanup, and
an explicit do-not list. Kept distinct from docs/release-workflows.md
(future release-mcp orchestrator). Link from README.

Documentation only; no code behavior changed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

README.md

@@ -186,6 +186,9 @@ Notes:
   [`docs/llm-workflow-runbooks.md`](docs/llm-workflow-runbooks.md) for the
   task-scoped, profile-based runbooks (create/review/merge/close, thin
   launchers, migration, fail-closed rules).
+- See [`docs/release-version-sop.md`](docs/release-version-sop.md) for the
+  operator SOP on cutting a versioned release (version bump, checks, merge,
+  `scripts/release-tag`, and cleanup).
 - For the **portable** version of this workflow (issue-first, isolated
   worktrees, no self-review/merge, profile safety, cleanup, fail-closed) that
   can be copied into any project, see the reusable skill