Add learn and teach skill library

[wmdmark]

What changed

• rename the personal learning skill from path to learn
• add the reusable multi-learner teach skill
• add a shared PathMX library of patterns, templates, components, and fictional examples
• document and fixture Lucide icons and the upcoming authored styling-class contract
• add bounded subagent orchestration at map review, module authoring, and checkpoints
• make skill synchronization transactional and retire the old managed path package

Why

Personal adaptive learning and reusable teaching paths need separate workflows while sharing one verified PathMX authoring library. The learner loop also needs a faster module-building lane without moving learner conversation or durable placement decisions into workers.

Verification

• bun run check
• 61 tests passed
• forward-tested a three-session fictional SQL module with separate Session 2 and Session 3 workers, focused checks, full integration, route resolution, and Player smoke