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/scss/theme.scss

@@ -110,17 +110,27 @@ $header-bg-opacity: 1;
 .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;
 
-    &:hover {
+    &:hover, &:focus {
         background-color: rgba(255, 255, 255, 0.1) !important;
         color: var(--header-font) !important;
     }
 }
 
+// Remove Bootstrap dropdown border/spacing on nav-tabs dropdown
+.nav-tabs .dropdown-menu {
+    margin-top: 0 !important;
+}
+
 // Hide Bootstrap dropdown arrow and use custom icon
 .dropdown-toggle::after {
     display: none !important;
@@ -287,6 +297,61 @@ $header-bg-opacity: 1;
     }
 }
 
+// Bootstrap 5 nested dropdown support (dropdown-submenu) — unlimited depth, CSS hover
+.dropdown-submenu {
+    position: relative;
+
+    > .dropdown-menu {
+        top: 0;
+        left: 100%;
+        margin-top: -1px;
+        margin-left: 0;
+        display: none;
+        border-radius: 0 !important;
+    }
+
+    // Open submenu on hover (desktop)
+    &:hover > .dropdown-menu {
+        display: block;
+    }
+
+    // Keep parent highlighted when hovering submenu
+    &:hover > .dropdown-toggle {
+        background-color: rgba(255, 255, 255, 0.15) !important;
+    }
+
+    // Arrow pointing right
+    > .dropdown-toggle .bi-chevron-right {
+        float: right;
+        margin-top: 0.25rem;
+    }
+}
+
+// Ensure dropdown items fill width and no gaps
+.dropdown-menu .dropdown-item {
+    width: 100%;
+    white-space: nowrap;
+}
+
+// Mobile: submenu appears below instead of beside, open on tap
+@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;
+    }
+}
+
 // Sidebar styling
 .sidebar-column {
     background-color: var(--sidebar-bg) !important;