feat(notifications): Implement functional header notification dropdown

This commit replaces the static notification dropdown in the header with a fully functional component that fetches live data from the API.

Key features include:
- Fetches and displays the latest notifications.
- Shows a badge with the count of unseen notifications.
- Opens a modal with notification details upon clicking an item.
- Marks notifications as seen when they are viewed.

Additionally, this commit includes several related improvements:
- refactor: Replaced the global loading component with a custom Tailwind CSS spinner for a consistent look and feel.
- feat: Enhanced the DatePicker component to optionally include a time picker.
- style: Improved the layout of the notification details page by moving the message to a dedicated section and capitalizing the 'priority' and 'type' fields for better readability.

src/components/forms/notifications/CreateNotification.tsx

@@ -51,6 +51,7 @@ const CreateNotificationForm = () => {
             name="schedule_at"
             label="schedule at"
             range={false}
+            timePicker
             placeholder="Select schedule date"
           />
         </div>
@@ -100,7 +101,7 @@ const CreateNotificationForm = () => {
             {...register("link", {
               pattern: {
                 value: REGEX.URL,
-                message: FormErrorMessages.invalidPattern, 
+                message: FormErrorMessages.invalidPattern,
               },
             })}
             name="link"
@@ -152,7 +153,13 @@ const CreateNotificationForm = () => {
         </div>
         <div className="col-span-2 flex flex-col gap-2">
           <TextAreaGroup
-            {...register("description")}
+            required
+            {...register("description", {
+              required: {
+                value: true,
+                message: FormErrorMessages.required,
+              },
+            })}
             label="Description"
             name="description"
             placeholder="Enter description"