fix: Search rake task causing Rails boot error (#12416)

## Description

This PR sets up an `Enterprise::Railtie` to correctly register rake
tasks in the `enterprise` namespace.
Previously, rake tasks under `enterprise/lib/tasks` were being eagerly
loaded at Rails boot, causing `undefined method 'namespace'` errors.

With this change, rake tasks are now registered only in the rake
context, avoiding boot-time issues and ensuring they are discoverable
with `bin/rake -T`.

**Tasks added:**

* `search:all` → Reindex messages for all accounts
* `search:account[ID]` → Reindex messages for a specific account

Fixes: #12414


Co-authored-by: Sojan Jose <sojan@pepalo.com>

enterprise/tasks_railtie.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class TasksRailtie < Rails::Railtie
+  rake_tasks do
+    # Load all rake tasks from enterprise/lib/tasks
+    Dir.glob(Rails.root.join('enterprise/lib/tasks/**/*.rake')).each { |f| load f }
+  end
+end