Fix Settings app layout for RmlUi flex rendering

Add explicit width and flex container properties to fix elements
collapsing to zero width in RmlUi:
- .settings-list: Add width: 100%, display: flex, flex-direction: column
- .settings-section: Add width: 100%, display: flex, flex-direction: column
- .settings-item: Add width: 100%, box-sizing: border-box
- .user-card: Add width: 100%, box-sizing: border-box

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/main/assets/apps/settings/settings.rml

@@ -17,10 +17,16 @@
         .settings-list {
             flex: 1;
             overflow: auto;
+            width: 100%;
+            display: flex;
+            flex-direction: column;
         }
 
         .settings-section {
             margin-bottom: 8px;
+            width: 100%;
+            display: flex;
+            flex-direction: column;
         }
 
         .settings-header {
@@ -36,6 +42,8 @@
             padding: 16px;
             cursor: pointer;
             background-color: #1E1E1E;
+            width: 100%;
+            box-sizing: border-box;
         }
 
         .settings-item:hover {
@@ -117,6 +125,8 @@
             padding: 20px 16px;
             background-color: #1E1E1E;
             margin-bottom: 8px;
+            width: 100%;
+            box-sizing: border-box;
         }
 
         .user-avatar {