refactor : migrate UI to Malio layer-ui components (MalioButton, MalioDrawer, MalioSelectCheckbox)

- Replace all AppDrawer with MalioDrawer across 10 drawer components
- Replace native <button> with MalioButton/MalioButtonIcon in all pages and components
- Fix TimeTrackingExportDrawer: use MalioSelectCheckbox for multi-select filters
- Add Malio design system colors (m-btn-*, m-disabled, m-surface) to tailwind.config.ts
- Align toggle button heights with MalioButton (h-[40px])

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/components/notification/NotificationBell.vue

@@ -1,18 +1,21 @@
 <template>
     <div ref="bellRef" class="relative">
-        <button
-            type="button"
-            class="relative rounded-md p-2 text-white hover:bg-primary-600 transition-colors"
-            @click="toggleDropdown"
-        >
-            <Icon name="mdi:bell-outline" size="24" />
+        <div class="relative">
+            <MalioButtonIcon
+                icon="mdi:bell-outline"
+                aria-label="Notifications"
+                variant="ghost"
+                icon-size="24"
+                button-class="text-white hover:bg-primary-600"
+                @click="toggleDropdown"
+            />
             <span
                 v-if="unreadCount > 0"
-                class="absolute -right-0.5 -top-0.5 flex h-5 min-w-5 items-center justify-center rounded-full bg-red-500 px-1 text-xs font-bold text-white"
+                class="absolute -right-0.5 -top-0.5 flex h-5 min-w-5 items-center justify-center rounded-full bg-red-500 px-1 text-xs font-bold text-white pointer-events-none"
             >
                 {{ unreadCount > 99 ? '99+' : unreadCount }}
             </span>
-        </button>
+        </div>
 
         <Transition name="dropdown">
             <div