docs(router): add model-to-skill-ID mapping table

The router names models by display name only, so an agent that routed
successfully still has to guess the invocable skill ID - and several
slugs are not the lowercased display name (Systems Thinking ->
thinking-systems, 5 Whys Plus -> thinking-five-whys-plus). The table
lets routing end in an exact thinking-skills:thinking-<slug> call.

Claude-Session: https://claude.ai/code/session_01WxvtAd56PQLSDsGg2n1DAE