fix: add width constraints to prevent horizontal overflow on mobile

Added max-width: 100% and overflow-x: hidden to main-content and cospend-main containers to prevent child elements from forcing horizontal scroll on mobile devices.

src/routes/cospend/+layout.svelte

@@ -81,6 +81,8 @@
 
   .main-content {
     flex: 1;
+    max-width: 100%;
+    overflow-x: hidden;
     transition: margin-right 0.3s ease-out;
   }
 

src/routes/cospend/+page.svelte

@@ -275,6 +275,8 @@
   .cospend-main {
     margin: 0 auto;
     padding: 2rem;
+    max-width: 100%;
+    overflow-x: hidden;
   }
 
   h1 {