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/config/schema/commands.ts

@@ -8,6 +8,7 @@ export const BuiltinCommandNameSchema = z.enum([
   "refactor",
   "start-work",
   "stop-continuation",
+  "remove-ai-slops",
 ])
 
 export type BuiltinCommandName = z.infer<typeof BuiltinCommandNameSchema>