Tech debt: define mise's usage boundary

Tracked in `roadmap.md` *Tech debts* as: **"Define mise usage"**

`mise` is used for pinned toolchain management in generated projects, but its boundary is not written down anywhere — which tools it owns, what stays in `Makefile`, and what a contributor may add.

Directly connected to the open question on **Production Containerization**: whether `mise`-managed toolchains are still needed inside a production image or can be dropped for a leaner runtime stage. Answering that answers half of this.

Start with the Tech debts entry in roadmap.md, then inspect how mise and the Makefile are used for toolchain management in generated projects. Resolve which tools belong to mise, which stay in the Makefile, what contributors may add, and whether production images need mise-managed toolchains; done means these boundaries and the containerization decision are documented.

Written by the indexing model from the issue text.