[Chore] Generate release docs on zoo-stable-release dispatch

[zoomote]

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What changed

Adds the receiver side of the docs-release automation:

• .github/workflows/zoo-stable-release.yml — triggers on repository_dispatch (types: [zoo-stable-release]) sent by Zoo-Code after a stable publish. It validates the payload, runs pnpm docs:release, then typecheck + lint + unused-import lint + full Docusaurus build, and — on success — commits the generated release docs to main with the same-repo GITHUB_TOKEN. The push to main is what publishes to docs.zoocode.dev through the existing deployment pipeline. Concurrency is keyed on the release tag so duplicate dispatches queue instead of racing.
• scripts/docs-release.mjs (new pnpm docs:release script) — a deterministic, dependency-free generator that:
  • creates docs/update-notes/vX.Y.Z.mdx if missing (existing pages are never rewritten — human enrichment lands in reviewed PRs),
  • inserts the release into docs/update-notes/index.md and the "Extension Release Notes" category in sidebars.ts, newest-first (single-line sidebar categories are normalized to multi-line first),
  • syncs package.json version to the extension version, never downgrading,
  • is idempotent: re-running with the same payload produces no changes, so dispatch retries are safe.

Why this change was made

Publishing a stable extension currently requires manual release-notes bookkeeping in this repo. The Zoo-Code publisher now dispatches version, tag, source_sha, release_url (and the extracted changelog section as changes) so the mechanical parts happen automatically and consistently.

Impact

No change to existing docs content or site behavior today; the new workflow only runs on the dispatch event. Evergreen docs and enriched prose are intentionally not auto-rewritten — the automation is limited to the deterministic release-notes/index/version updates, and the generated notes page carries a comment directing enrichment edits to reviewed PRs. If branch protection blocks direct pushes to main, the final workflow step should be switched to an auto-merge PR flow (noted in a workflow comment).

Validation: pnpm run check-types, pnpm run lint, pnpm run lint:unused, and pnpm run build all pass. The generator was dry-run end-to-end against a scratch copy of this repo (new minor, patch into existing category, older-minor insertion, no-downgrade, idempotent re-run) with the resulting site passing tsc --noEmit and a full Docusaurus build; both workflow files pass actionlint.

Related PRs

• Zoo-Code-Org/Zoo-Code: [Chore] Trigger docs release via repository_dispatch after stable publish Zoo-Code#1898