Improve UI design system and fix notification positioning

- Overhaul CSS with comprehensive design tokens (shadows, transitions, radii)
- Add hover effects and smooth transitions to cards, buttons, tables
- Improve typography hierarchy and color consistency
- Remove inline styles from 10 template files for better maintainability
- Add global notification container to ensure toasts appear above modals
- Update showNotification/showAlert functions to use centralized container
- Add accessibility improvements (focus states, reduced motion support)
- Improve responsive design and mobile styling
- Add print styles

app/web/templates/webhooks/list.html

@@ -5,7 +5,7 @@
 {% block content %}
 <div class="row mt-4">
     <div class="col-12 d-flex justify-content-between align-items-center mb-4">
-        <h1 style="color: #60a5fa;">Webhook Management</h1>
+        <h1>Webhook Management</h1>
         <a href="{{ url_for('webhooks.new_webhook') }}" class="btn btn-primary">
             <i class="bi bi-plus-circle"></i> Add Webhook
         </a>