fix: sync agent tier when /model command switches model

The /model command was only updating the router's currentTier but not
the agent's currentTier. Since NativeAgent.chatWithRouter() passes its
own tier to router.chat(), switching to 'local' still sent requests
through the default (Anthropic) client first.

src/frontends/tui/minimal.ts

@@ -213,6 +213,10 @@ export class MinimalTui {
 
     const tier = resolveModelAlias(name);
     if (router.setTier(tier)) {
+      // Also update the agent tier so chatWithRouter uses the correct client
+      if (this.config.agent) {
+        this.config.agent.setModelTier(tier);
+      }
       console.log(`${colors.gray}Switched to model:${colors.reset} ${tier}\n`);
     } else {
       console.log(`${colors.gray}Model not available:${colors.reset} ${name}\n`);