fix: expose one active path per suite command

[filipeforattini]

Summary

• keep mise shims only as the non-activated shell fallback
• expose real mise tool directories once in activated shells
• keep RedSkills runtime commands on the signed active-set launchers
• retire the recognized legacy ~/.local/bin/rsp only after its replacement exists

Verification

• git diff --check
• local behavioral shell diagnostic: each first-party command resolves once before and after a mise hook
• full typecheck/test/build intentionally delegated to CI on this low-resource workstation

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