Set theme colour

This meta tag is used to set the colour that you see when the browse
'bounces':

https://webkit.org/blog/11989/new-webkit-features-in-safari-15/

it is currently set to `blue` which is pretty distracting!

In the current GOV.UK front end it is set to `#0b0c0c` so we do the
same:

https://design-system.service.gov.uk/styles/page-template/

CHANGELOG.md

@@ -4,6 +4,8 @@
 
 [Full changelog][unreleased]
 
+- theme colour has changed from blue to a black
+
 ## Release 156 - 2024-12-12
 
 [Full changelog][156]

app/views/layouts/application.html.haml

@@ -11,9 +11,10 @@
     %meta{charset: "utf-8"}/
     %title #{content_for :page_title_prefix} - #{t('app.title')}
     %meta{content: "width=device-width, initial-scale=1", name: "viewport"}/
-    %meta{content: "blue", name: "theme-color"}/
+    %meta{content: "#0b0c0c", name: "theme-color"}/
     %link{href: asset_path("favicon.ico"), rel: "shortcut icon", type: "image/x-icon"}/
 
+
     /[if !IE 8]
     = stylesheet_link_tag 'application', media: 'all'
     /[if lt IE 9]