fix(tui): enable tool access in fullscreen mode via NativeAgent

Fullscreen TUI was calling modelClient directly, bypassing the NativeAgent
tool loop entirely. Pass the agent through FullscreenTuiConfig → App and
use agent.process() for message handling, which enables the full tool
registry and executor.

src/cli/tui.ts

@@ -216,6 +216,7 @@ export function registerTuiCommand(program: Command): void {
           modelRouter,
           systemPrompt,
           model: config.models.default.model,
+          agent,
           onExit: cleanup,
         });
       } else {
@@ -259,6 +260,7 @@ export function registerTuiCommand(program: Command): void {
             modelRouter,
             systemPrompt,
             model: config.models.default.model,
+            agent,
             onExit: cleanup,
           });
           return;