feat: add review-work and ai-slop-remover as built-in skills, add remove-ai-slops command

Embed user-level skills into the plugin's built-in system so they ship
with the product rather than requiring per-user configuration.

- review-work: 5-agent parallel post-implementation review orchestrator
- ai-slop-remover: per-file AI-generated code smell detector and remover
- /remove-ai-slops: command that orchestrates parallel ai-slop-remover runs

src/features/builtin-skills/skills/index.ts

@@ -3,3 +3,5 @@ export { playwrightCliSkill } from "./playwright-cli"
 export { frontendUiUxSkill } from "./frontend-ui-ux"
 export { gitMasterSkill } from "./git-master"
 export { devBrowserSkill } from "./dev-browser"
+export { reviewWorkSkill } from "./review-work"
+export { aiSlopRemoverSkill } from "./ai-slop-remover"