kpn load: Ollama-mallin vaihto lennossa (0.5b → 32b)

- Hub: uusi POST /api/v1/model endpoint, broadcastaa change_model
- Native node: kuuntelee change_model, kutsuu Ollaman pull + vaihtaa mallin
- Frontend: kpn load näyttää 5 mallia, numero vaihtaa Ollaman mallin
- Selain-WASM pysyy 0.5B:nä (kpn load 1)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

network-poc/hub/src/main.rs

@@ -384,6 +384,7 @@ async fn main() {
         .route("/api/pairs", get(api_pairs))
         .route("/api/stats", get(api_stats))
         .route("/api/v1/chat/completions", axum::routing::post(api_chat_completions))
+        .route("/api/v1/model", axum::routing::post(api_change_model))
         .route("/admin", get(admin_page))
         .nest_service("/", {
             let static_dir = std::env::var("STATIC_DIR").unwrap_or_else(|_| "../static".to_string());
@@ -958,6 +959,20 @@ struct ChatCompletionResponse {
     tokens_generated: u64,
 }
 
+async fn api_change_model(
+    axum::extract::State(state): axum::extract::State<Arc<AppState>>,
+    axum::Json(payload): axum::Json<serde_json::Value>,
+) -> axum::response::Response {
+    let model = payload.get("model").and_then(|v| v.as_str()).unwrap_or("");
+    if model.is_empty() {
+        return (axum::http::StatusCode::BAD_REQUEST, "model puuttuu").into_response();
+    }
+    tracing::info!("Mallin vaihto: {}", model);
+    let msg = serde_json::json!({ "type": "change_model", "model": model });
+    let _ = state.stats_tx.send(msg.to_string());
+    axum::Json(serde_json::json!({ "status": "ok", "model": model })).into_response()
+}
+
 async fn api_chat_completions(
     axum::extract::State(state): axum::extract::State<Arc<AppState>>,
     ConnectInfo(addr): ConnectInfo<SocketAddr>,