87a3b163e7
First behavior-preserving slice of the Maven redesign. Establishes explicit ingress/routing boundaries and enough observability to refactor later without changing current routing, action, clarification, or execution semantics. Types introduced: - NormalizedInput (internal/router/source.go): Text + InputSource, the typed ingress boundary replacing raw string at the turn entry. - InputSource (internal/router/source.go): channel provenance enum (tap:voice, tap:text). Reuses the existing turnSource distinction. - RouteProducer (internal/router/intent.go): which cascade stage produced the decision (grammar, heads, llm, classifier). Changes: - Decision carries a Producer RouteProducer field, set at each cascade stage (grammar, heads, LLM, classifier). - turnRoute carries NormalizedInput instead of bare text string. - runTurn takes NormalizedInput instead of (text, src). - decision.Record carries InputSource and RouteProducer for observability; RoutingTrace persists route_producer (migration #27). - turnSource is now a type alias for router.InputSource. Behavior preserved: - Stage-0 grammars unchanged: same order, same matching, same confidence. - Cascade fallthrough order unchanged (grammar → heads → llm → classifier). - Clarification behavior unchanged. - Action dispatch unchanged. - No new linguistic normalization.