Add monorepo template support

[erkininfinity]

Goal

Add a monorepo template for repositories with multiple apps/packages.

Suggested scope

• Add template data for monorepo setup/test/build guidance.
• Include do-not-touch rules for workspace lockfiles and generated package outputs.
• Add tests that verify the template can generate all supported instruction targets.

Why this helps

Many OSS projects are monorepos, and agent instructions need workspace-aware commands.