cherrypick

Use whenever editing or adding code under `packages/backend/` — including REST API endpoints, NestJS services/modules, TypeORM entities, migrations, and backend tests. Covers NestJS DI patterns, TypeORM entity conventions, endpoint-list registration, meta/paramDef/res, misskey-js regeneration, migration up/down rules, and the `.config/test.yml` prerequisite. Must be consulted before any backend change to avoid CI failures and production incidents. This is NOT waived by having already invoked brainstorming, writing-plans, or any other upstream skill — invoke this at implementation time regardless of what preceded it.

Use whenever editing or adding code under `packages/frontend/`, or editing `locales/ja-JP.yml` for frontend-facing UI text — including Vue 3 SFCs (`Mk*` components), i18n keys (`i18n.ts.<key>` / `i18n.tsx.<key>()`), SCSS Modules, theme/CSS variables, `os.*` UI helpers, and Storybook stories. Covers SPDX (HTML comment form), `<script setup lang="ts">` conventions, type-only defineProps, `ja-JP.yml`-only locale editing (other locale yml files are Crowdin-managed and must not be edited), and accessibility. Must be consulted before any frontend or UI-locale change to avoid CI failures, lost translations, and reviewer pushback. This is NOT waived by having already invoked brainstorming, writing-plans, or any other upstream skill — invoke this at implementation time regardless of what preceded it.