feat(sidebar): collapse to icon rail, expand on hover

Sidebar is icon-only by default and expands as an overlay on hover, so the dashboard content underneath no longer reflows. Drops the persisted collapse state and the click trigger that conflicted with hover.

frontend/src/layouts/AppSidebar.css

@@ -5,6 +5,20 @@
   align-self: flex-start;
 }
 
+.ant-sidebar.is-rail {
+  flex: 0 0 80px;
+  width: 80px;
+  overflow: visible;
+}
+
+.ant-sidebar.is-rail > .ant-layout-sider {
+  z-index: 100;
+}
+
+.ant-sidebar.is-rail:hover > .ant-layout-sider {
+  box-shadow: 2px 0 16px rgba(0, 0, 0, 0.18);
+}
+
 .sider-brand,
 .drawer-brand {
   font-weight: 600;
@@ -245,6 +259,15 @@
     min-width: 0 !important;
     width: 0 !important;
   }
+
+  .ant-sidebar,
+  .ant-sidebar.is-rail {
+    flex: 0 0 0 !important;
+    width: 0 !important;
+    min-width: 0 !important;
+    max-width: 0 !important;
+    overflow: hidden !important;
+  }
 }
 
 body.dark .ant-drawer-content,