feat(stdlib): add WorkspaceTool for workspace discovery

[brunozoric]

Summary

• Add WorkspaceTool to @webiny/stdlib/node as a drop-in replacement for the get-yarn-workspaces package
• Walks up from a given cwd to find the nearest package.json with a workspaces field, resolves glob patterns using fast-glob.sync(), and returns { name, path }[] for each workspace
• Supports both flat array (workspaces: ["packages/*"]) and Yarn's object format (workspaces: { packages: ["packages/*"] })
• Zero new dependencies — uses fast-glob already in stdlib

Exports

Export	Description
WorkspaceTool	DI abstraction token ("Node/WorkspaceTool")
WorkspaceToolFeature	Registers WorkspaceTool in singleton scope
createWorkspaceTool()	Factory function for non-DI usage
listWorkspaces(params?)	Standalone function — direct replacement for getYarnWorkspaces()
WorkspaceRootNotFoundError	Thrown when no root with workspaces is found
WorkspaceInfo	{ name: string, path: string }
ListWorkspacesParams	{ cwd?: string }

Migration from get-yarn-workspaces

// Before
import getYarnWorkspaces from "get-yarn-workspaces";
const paths: string[] = getYarnWorkspaces();

// After
import { listWorkspaces } from "@webiny/stdlib/node";
const workspaces = listWorkspaces(); // { name, path }[]
const paths = workspaces.map(w => w.path); // if you need string[] only

Test plan

• Flat array workspaces format
• { packages: [] } object format
• Skips directories without package.json
• Falls back to folder name when package.json has no name field
• Walks up directory tree to find workspace root
• Multiple glob patterns
• Empty result when patterns match nothing
• Throws WorkspaceRootNotFoundError when no workspace root found
• Defaults cwd to process.cwd()
• Returns absolute paths
• Factory function (createWorkspaceTool)
• Standalone function (listWorkspaces)

12 tests added, 0 existing tests modified. Full pre-commit chain passes.