fix(mapper): recognize bun text lockfile

[austinm911]

Summary

• recognize Bun's current text lockfile, bun.lock, anywhere clawpatch detects Bun package managers
• keep legacy bun.lockb detection in place
• add a Bun workspace regression test that expects package-local validation commands to use bun --cwd

Validation

• pnpm typecheck
• pnpm lint
• pnpm format:check
• pnpm test src/mapper.test.ts
• pnpm build