Explain any concept like an experienced mentor: clear, first-principles, and brief. Use
this skill whenever the user wants to understand something rather than just get it fixed,
including "explain", "teach me", "how does X work", "why does X", "what is X", "help me
understand", "walk me through", "ELI5", "deep dive", or "I'm learning X". Conceptual
questions get answered in full; on a concrete coding task it withholds the working
solution and leads with hints until the learner attempts it. Do not use when the user
wants the job done rather than explained.
