Dark Mode & UI Improvements

This PR adds dark mode support to Devise views and improves overall UI organization.

Dark Mode Support

• Added dark mode styling across all Devise views
• Enhanced error_messages partial with proper dark mode colors
• Updated password reset views with dark mode compatibility
• Fixed styling in all Devise templates to support dark mode
• Add dark mode preference detection on top of app preference

Improved Table Navigation

• Converted "My Assignments" List/Table views to a tabbed interface
• Created scrollable containers that utilize available viewport height
• Applied sticky positioning to table headers in Table View
• Made date headers in List View sticky as well
• Added appropriate background colors to ensure sticky headers remain visible

User Profile Enhancements

• Grouped appearance settings (Theme Preference and Profile Color)
• Added better labels and helpful descriptions for settings
• Created a collapsible "Change Password" section (hidden by default)
• Made "More Languages Team only" section collapsible and collapsed by default
• Implemented measures to prevent browser autocomplete on password fields

app/views/assignments/_listview_date.html.erb

 <div class="mb-6 <%= Time.parse(date).end_of_day < now ? "past" : "future" %>">
-  <h3 class="text-lg font-semibold text-gray-700 dark:text-gray-300 mb-3"><%= date %></h3>
+  <h3 class="sticky top-0 z-10 text-lg font-semibold text-gray-700 dark:text-gray-300 mb-3 bg-white dark:bg-gray-800 py-2"><%= date %></h3>
   <ul class="space-y-3">
     <% assignments_on_date.each do |assignment| %>
       <li class="<%= assignment.session.starts_at < now ? "past" : "future" %> pl-4 border-l-4 border-gray-200 dark:border-gray-700">