feat: redmine_tonalmine plugin for default and per-account appearance

Admins set the default mode, contrast and color on Settings > Display,
shown as three labelled form rows below the Theme select. Logged-in
users' choices are saved on their account and override only the parts
they changed; anonymous visitors get the default.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

redmine_tonalmine/init.rb

@@ -0,0 +1,14 @@
+# Companion plugin for the Tonalmine theme: an administrator default appearance (set in
+# Administration > Settings > Display, below the theme select) and each user's appearance saved
+# on their account. The theme works without it; then the choice is stored per browser.
+Redmine::Plugin.register :redmine_tonalmine do
+  name 'Tonalmine'
+  author 'Andreas Reinhold'
+  description 'Default appearance and per-user appearance for the Tonalmine theme'
+  version '0.1.0'
+  requires_redmine version_or_higher: '7.0.0'
+  # No :partial: the default is edited on the Display settings tab (see theme.js).
+  settings default: {}
+end
+
+RedmineTonalmine::Hooks # loads and registers the hook listener