Update theme gem and document PLATFORM_NAME variable

Why these changes are being introduced:

The GDT project added a feature to the theme gem to conditionally
include the platform name in the header if the `PLATFORM_NAME`
environment variable is supplied.

Relevant ticket(s):

https://mitlibraries.atlassian.net/browse/GDT-124

How this addresses that need:

This updates the theme gem to the v1.2 tag, which includes the new
feature, and documents the PLATFORM_NAME variable. It also hides
the title in the navbar if PLATFORM_NAME is present.

Side effects of this change:

None. The app will continue to use the standard header if
PLATFORM_NAME is not supplied.

Author: jazairi

Gemfile

@@ -19,7 +19,7 @@ gem 'json'
 gem 'kaminari'
 gem 'lograge'
 gem 'marc'
-gem 'mitlibraries-theme', git: 'https://github.com/mitlibraries/mitlibraries-theme', tag: 'v1.1'
+gem 'mitlibraries-theme', git: 'https://github.com/mitlibraries/mitlibraries-theme', tag: 'v1.2'
 gem 'net-imap', require: false
 gem 'net-pop', require: false
 gem 'net-smtp', require: false

Gemfile.lock

@@ -1,7 +1,7 @@
 GIT
   remote: https://github.com/mitlibraries/mitlibraries-theme
-  revision: 93b931b802485f9e35a6878f957b3fd88ae3b294
-  tag: v1.1
+  revision: bcbe5d3de36a92d275085a045c5c4d8f30f33e62
+  tag: v1.2
   specs:
     mitlibraries-theme (1.0.2)
       rails (>= 6, < 8)

README.md

@@ -100,6 +100,8 @@ override easily with this ENV if you need to get more details.
 transfers and informs transfer submitters that the application is under maintenance.
 `MAINTENANCE_MESSAGE_TRANSFER` - provides a custom message to transfer submitters if more details are necessary.
 
+`PLATFORM_NAME`: The value set is added to the header after the MIT Libraries logo. The logic and CSS for this comes from our theme gem.
+
 `PREFERRED_DOMAIN` - set this to the domain you would like to use. Any other
 requests that come to the app will redirect to the root of this domain. This is
 useful to prevent access to herokuapp.com domains as well as any legacy domains

app/views/layouts/_site_nav.html.erb

@@ -1,8 +1,10 @@
 <div class="wrap-outer-header-local layout-band">
   <div class="wrap-header-local">
-    <div class="local-identity">
-      <h2 class="title title-site"><%= link_to "Thesis Submission at MIT Libraries", root_path %></h2>
-    </div>
+    <% unless ENV['PLATFORM_NAME'] %>
+      <div class="local-identity">
+        <h2 class="title title-site"><%= link_to "Thesis Submission at MIT Libraries", root_path %></h2>
+      </div>
+    <% end %>
     <div class="wrap-local-nav">
       <div class="wrap-bar">
         <nav class="local-nav" aria-label="Main menu">