feat(butler): upgrade ButlerRouter to semantic skill routing

Replace keyword-only ButlerRouter with SemanticSkillRouter (TF-IDF).
75 skills now participate in intent classification instead of 4 hardcoded domains.

- Expose ButlerRouterBackend trait + RoutingHint as pub
- Add with_router() constructor for injecting custom backends
- Add SemanticRouterAdapter in kernel layer (bridges skills ↔ runtime)
- Enhance context injection with skill-level match info

crates/zclaw-kernel/src/kernel/mod.rs

@@ -193,7 +193,40 @@ impl Kernel {
         // Butler router — semantic skill routing context injection
         {
             use std::sync::Arc;
-            let mw = zclaw_runtime::middleware::butler_router::ButlerRouterMiddleware::new();
+            use zclaw_runtime::middleware::butler_router::{ButlerRouterBackend, RoutingHint};
+            use async_trait::async_trait;
+            use zclaw_skills::semantic_router::SemanticSkillRouter;
+
+            /// Adapter bridging `SemanticSkillRouter` (zclaw-skills) to `ButlerRouterBackend`.
+            /// Lives here in kernel because kernel depends on both zclaw-runtime and zclaw-skills.
+            struct SemanticRouterAdapter {
+                router: Arc<SemanticSkillRouter>,
+            }
+
+            impl SemanticRouterAdapter {
+                fn new(router: Arc<SemanticSkillRouter>) -> Self {
+                    Self { router }
+                }
+            }
+
+            #[async_trait]
+            impl ButlerRouterBackend for SemanticRouterAdapter {
+                async fn classify(&self, query: &str) -> Option<RoutingHint> {
+                    let result: Option<_> = self.router.route(query).await;
+                    result.map(|r| RoutingHint {
+                        category: "semantic_skill".to_string(),
+                        confidence: r.confidence,
+                        skill_id: Some(r.skill_id),
+                    })
+                }
+            }
+
+            // Build semantic router from the skill registry (75 SKILL.md loaded at boot)
+            let semantic_router = SemanticSkillRouter::new_tf_idf_only(self.skills.clone());
+            let adapter = SemanticRouterAdapter::new(Arc::new(semantic_router));
+            let mw = zclaw_runtime::middleware::butler_router::ButlerRouterMiddleware::with_router(
+                Box::new(adapter)
+            );
             chain.register(Arc::new(mw));
         }