bug: pnpm-workspace.yaml not detected by validate and edit-package-json commands

[WolfieLeader]

Description

After #85, monorepo detection in validate and edit-package-json commands does not recognize pnpm-workspace.yaml. This causes:

1. commands/validate.ts: isInsideMonorepo() only walks up checking package.json workspaces fields — pnpm monorepos using pnpm-workspace.yaml (without a workspaces field in package.json) are missed, producing false !skills/_artifacts packaging warnings.

2. setup.ts runEditPackageJson(): Has the same blind spot in its inline monorepo detection IIFE — it incorrectly adds !skills/_artifacts to the files array for pnpm monorepo packages.

Expected Behavior

Both commands should detect monorepos via findWorkspaceRoot() → readWorkspacePatterns(), which already handles pnpm-workspace.yaml, package.json workspaces, and other formats.

Reproduction

1. Create a pnpm monorepo with pnpm-workspace.yaml (no workspaces field in root package.json)
2. Add skills to a workspace package
3. Run intent validate packages/<pkg>/skills — observe false !skills/_artifacts warning
4. Run intent edit-package-json from a workspace package — observe !skills/_artifacts incorrectly added to files