Refactor navigation logic to be consistent and strict

app.py

@@ -1145,11 +1145,8 @@ with gr.Blocks(title="AnatomyBot - MBBS Anatomy Tutor") as demo:
             student_name_state  # Return student name (unchanged)
         ]
     ).then(
-        fn=lambda: (gr.update(visible=False), gr.update(visible=True), gr.update(visible=False), gr.update(visible=False)),
-        outputs=[learning_col, viva_col, book_col, admin_col]
-    ).then(
-        fn=lambda: (gr.update(variant="secondary"), gr.update(variant="primary"), gr.update(variant="secondary"), gr.update(variant="secondary")),
-        outputs=[nav_learning_btn, nav_viva_btn, nav_book_btn, nav_admin_btn]
+        fn=lambda: navigate("viva"),
+        outputs=[learning_col, viva_col, book_col, admin_col, nav_learning_btn, nav_viva_btn, nav_book_btn, nav_admin_btn]
     ).then(
         fn=lambda: gr.update(value="🎯 Start VIVA Training", interactive=True),  # Reset button
         outputs=[start_viva_btn]
@@ -1241,11 +1238,8 @@ with gr.Blocks(title="AnatomyBot - MBBS Anatomy Tutor") as demo:
             question_audio, viva_greeting, student_name_state
         ]
     ).then(
-        fn=lambda: (gr.update(visible=False), gr.update(visible=True), gr.update(visible=False), gr.update(visible=False)),
-        outputs=[learning_col, viva_col, book_col, admin_col]
-    ).then(
-        fn=lambda: (gr.update(variant="secondary"), gr.update(variant="primary"), gr.update(variant="secondary"), gr.update(variant="secondary")),
-        outputs=[nav_learning_btn, nav_viva_btn, nav_book_btn, nav_admin_btn]
+        fn=lambda: navigate("viva"),
+        outputs=[learning_col, viva_col, book_col, admin_col, nav_learning_btn, nav_viva_btn, nav_book_btn, nav_admin_btn]
     ).then(
         fn=lambda: 0,
         outputs=[current_question_idx]