fix: mobile menu full-width separator lines (100vw menu + box-shadow)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: troke12

frontend/src/components/Navbar.css

@@ -127,7 +127,7 @@ a.btn-nav {
   font-size: 1.25rem;
 }
 
-/* Mobile Menu */
+/* Mobile Menu - full viewport width so separator lines span edge-to-edge */
 .navbar-menu-mobile {
   display: none;
   flex-direction: column;
@@ -137,6 +137,9 @@ a.btn-nav {
   max-height: 0;
   overflow: hidden;
   transition: max-height 0.25s ease;
+  width: 100vw;
+  margin-left: calc(-50vw + 50%);
+  box-sizing: border-box;
 }
 
 .navbar-menu-mobile.open {
@@ -151,7 +154,6 @@ a.btn-nav {
   font-size: 0.9375rem;
   transition: var(--transition);
   border: none;
-  border-bottom: 1px solid rgba(255, 255, 255, 0.1);
   background: transparent;
   color: white;
   text-align: left;
@@ -161,6 +163,14 @@ a.btn-nav {
   cursor: pointer;
   width: 100%;
   -webkit-tap-highlight-color: transparent;
+  box-sizing: border-box;
+  position: relative;
+  /* Full-width separator via box-shadow so it always spans the full menu width */
+  box-shadow: inset 0 -1px 0 0 rgba(255, 255, 255, 0.15);
+}
+
+.btn-nav-mobile:last-child {
+  box-shadow: none;
 }
 
 .btn-nav-mobile:hover:not(:disabled) {