Lift inline routing_preferences under each model_provider into the
top-level routing_preferences list with merged models[] and bump
version to v0.4.0, with a deprecation warning. Existing v0.3.0
demo configs (Claude Code, Codex, preference_based_routing, etc.)
keep working unchanged. Schema flags the inline shape as deprecated
but still accepts it. Docs and skills updated to canonical top-level
multi-model form.
