[UX] app.py: British spelling (Optimizer -> Optimiser, Optimization -> Optimisation)

app.py

@@ -49,7 +49,7 @@ if os.path.exists(csv):
         st.cache_data.clear()
         st.rerun()
 
-st.set_page_config("Carbon Portfolio Optimizer", layout="wide")
+st.set_page_config("Carbon Portfolio Optimiser", layout="wide")
 
 def load_css(file_path):
     with open(file_path) as f:
@@ -58,7 +58,7 @@ def load_css(file_path):
 css_path = pathlib.Path("assets/styles.css")
 load_css(css_path)
 
-st.markdown('<h1 class="custom-title">CRRA <span class="crra-hl-toolkit">Toolkit</span>: CDR Portfolio Optimization</h1>', unsafe_allow_html=True)
+st.markdown('<h1 class="custom-title">CRRA <span class="crra-hl-toolkit">Toolkit</span>: CDR Portfolio Optimisation</h1>', unsafe_allow_html=True)
 
 _NAV_OPTIONS = [
     "Welcome",