New option to require subcommand

[aaronadamsCA]

I'd like to add a setting that disables the shorthand pnpm <command> and forces usage of the more explicit pnpm run <command> and pnpm exec <command>.

The context is LLM agents and newer developers. The shorthand obfuscates the distinction between scripts, executables, and pnpm built-ins. IMHO this steepens the learning curve, and it would be better to force explicit invocation to help them understand the system.

We had a script named clean for a long time, then you added a pnpm clean command, and it turned out a lot of our devs and agents couldn't tell why the behaviour had changed.