Introduce Dark Mode

This commit mainly changes the color definitions. Mostly, those changes are semantically equally, but there are a few changes that occurred to align the color scheme within the app.

app/views/application/_breadcrumbs_and_title.html.slim

@@ -20,7 +20,7 @@
 - title = "#{active_action} - #{application_name}"
 - content_for :breadcrumbs do
   .container.mb-4
-    ul.breadcrumb.bg-light.px-3.py-2
+    ul.breadcrumb.bg-body-secondary.px-3.py-2
       - if root_element.present?
         li.breadcrumb-item.small
           = root_element

app/views/application/_color_mode_selector.html.slim

@@ -0,0 +1,17 @@
+li.nav-item.dropdown
+  a.nav-link.dropdown-toggle.me-3 data-bs-toggle='dropdown' href='#'
+    = t('shared.color_mode.title')
+    span.caret
+  ul.dropdown-menu.p-0.mt-1 role='menu'
+    li
+      button.dropdown-item.d-flex.align-items-center data={ 'bs-theme-value': 'light' }
+        i.fa-fw.fa-solid.fa-sun
+        = t('shared.color_mode.light')
+    li
+      button.dropdown-item.d-flex.align-items-center data={ 'bs-theme-value': 'dark' }
+        i.fa-fw.fa-solid.fa-moon
+        = t('shared.color_mode.dark')
+    li
+      button.dropdown-item.d-flex.align-items-center data={ 'bs-theme-value': 'auto' }
+        i.fa-fw.fa-solid.fa-wand-magic-sparkles
+        = t('shared.color_mode.auto')

app/views/application/_locale_selector.html.slim

@@ -1,5 +1,5 @@
 li.nav-item.dropdown
-  a.nav-link.dropdown-toggle.mx-3 data-bs-toggle='dropdown' href='#'
+  a.nav-link.dropdown-toggle.me-3 data-bs-toggle='dropdown' href='#'
     = t("locales.#{I18n.locale}")
     span.caret
   ul.dropdown-menu.p-0.mt-1 role='menu'