feat: Add yarn workspace / yarn monorepo support (Turborepo pattern)

Summary

rtk discover shows yarn workspace as the most frequent unhandled command
in my project — 194 calls in 30 days, more than find (148) or ls (179).
Currently all output goes unfiltered into Claude's context.

Environment

• Package manager: yarn workspaces (Turborepo monorepo)
• Project type: TypeScript + Next.js + Fastify + Drizzle ORM
• RTK version: 0.24.0

Commands from discover output (unhandled)

Why it matters

In a Turborepo monorepo, yarn workspace <name> typecheck 2>&1 produces
large TypeScript compiler traces across multiple packages. Without filtering,
every typecheck dumps full tsc output into context — same problem that
rtk tsc solves for direct npx tsc calls.

Expected savings (based on rtk tsc ~11.7K tokens / 32 calls ratio):
194 yarn calls × ~365 tokens avg = ~70K tokens/month for yarn workspace alone.

Expected behavior

RTK should intercept and filter yarn commands similarly to existing handlers:

# Typecheck — route through rtk tsc filter
yarn workspace api typecheck  →  rtk tsc (errors grouped by file)

# Tests — route through rtk test filter  
yarn workspace api test       →  rtk test (failures only)
yarn test                     →  rtk test (failures only)

# Install — strip progress bars, show only errors
yarn install                  →  rtk err yarn install

# Add packages — compact output
yarn add -D husky             →  show only final installed versions

Workaround (current)

rtk err yarn workspace api typecheck
rtk test yarn workspace api test

Works but requires manual prefix — defeats the purpose of hook-based automation.

Request

1. Add yarn as a recognized command in rtk rewrite routing
2. Sub-route yarn workspace <name> typecheck → tsc filter
3. Sub-route yarn workspace <name> test / yarn test → test filter
4. Sub-route yarn install / yarn add → err filter (progress bars stripped)

Happy to test a PR — Turborepo + yarn workspaces setup available.

Start with the rtk rewrite routing entry point and inspect the existing tsc, test, and err filters. Trace how commands are classified and routed, then verify that the requested yarn workspace, test, install, and add forms produce the corresponding filtered output.