[UX] tab6_scenarios.py: British spelling (optimization -> optimisation)

tabs/tab6_scenarios.py

@@ -175,7 +175,7 @@ def render_tab():
     panel_load_scenario()
 
     if not st.session_state.scenarios:
-        st.info("No scenarios saved yet. Run an optimization in **Portfolio generation** tab and **save the scenario** or load a file above.", icon=":material/info:")
+        st.info("No scenarios saved yet. Run an optimisation in **Portfolio generation** tab and **save the scenario** or load a file above.", icon=":material/info:")
         return
 
     # Select & manage scenarios