Fix dropdown menu styling: no rounded corners, no gaps, consistent hover

- border-radius: 0 on all dropdown-menu and dropdown-item
- padding: 0 and margin: 0 on dropdown-menu
- margin-left: 0 on submenu (no gap between parent and child)
- margin-top: -1px on submenu (seamless border overlap)
- CSS hover opens submenu on desktop, click on mobile
- white-space: nowrap on dropdown items
- Fix statistics getFullStats -> getStats
- Fix Twig ?? operator -> default filter on dashboard/statistics
- Asset server (public/asset.php) for production static file serving
- .htaccess rewrite rules for themes/admin/plugins assets

themes/default/assets/css/theme.css

@@ -71,15 +71,22 @@
 .dropdown-menu {
   background-color: var(--header-bg) !important;
   border: 1px solid var(--header-font) !important;
+  border-radius: 0 !important;
+  padding: 0 !important;
+  margin: 0 !important;
 }
-
 .dropdown-item {
   color: var(--header-font) !important;
+  border-radius: 0 !important;
+  padding: 0.5rem 1rem;
 }
-.dropdown-item:hover {
+.dropdown-item:hover, .dropdown-item:focus {
   background-color: rgba(255, 255, 255, 0.1) !important;
   color: var(--header-font) !important;
 }
+.nav-tabs .dropdown-menu {
+  margin-top: 0 !important;
+}
 
 .dropdown-toggle::after {
   display: none !important;
@@ -287,6 +294,50 @@ pre code {
   line-height: 1.5;
 }
 
+/* Bootstrap 5 nested dropdown support (dropdown-submenu) — unlimited depth, CSS hover */
+.dropdown-submenu {
+  position: relative;
+}
+.dropdown-submenu > .dropdown-menu {
+  top: 0;
+  left: 100%;
+  margin-top: -1px;
+  margin-left: 0;
+  display: none;
+  border-radius: 0 !important;
+}
+.dropdown-submenu:hover > .dropdown-menu {
+  display: block;
+}
+.dropdown-submenu:hover > .dropdown-toggle {
+  background-color: rgba(255, 255, 255, 0.15) !important;
+}
+.dropdown-submenu > .dropdown-toggle .bi-chevron-right {
+  float: right;
+  margin-top: 0.25rem;
+}
+.dropdown-menu .dropdown-item {
+  width: 100%;
+  white-space: nowrap;
+}
+@media (max-width: 767.98px) {
+  .dropdown-submenu > .dropdown-menu {
+    left: 0;
+    top: 100%;
+    margin-top: 0;
+    margin-left: 1rem;
+    border: none;
+    border-left: 2px solid rgba(255, 255, 255, 0.2);
+    box-shadow: none;
+  }
+  .dropdown-submenu:hover > .dropdown-menu {
+    display: none;
+  }
+  .dropdown-submenu.show > .dropdown-menu {
+    display: block;
+  }
+}
+
 code {
   background: #e8e8e8;
   padding: 0.15rem 0.4rem;