feat: add ops task to purge orphan conversations (#12279)

## Summary

Add ops task to find and remove conversations missing contacts or
inboxes. You can run this via

```
bundle exec rake chatwoot:ops:cleanup_orphan_conversations
```
 
 
fixes:
https://linear.app/chatwoot/issue/CW-5439/conversations-missing-contacts

lib/tasks/ops/cleanup_orphan_conversations.rake

@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+# Run with:
+#   bundle exec rake chatwoot:ops:cleanup_orphan_conversations
+
+namespace :chatwoot do
+  namespace :ops do
+    desc 'Identify and delete conversations without a valid contact or inbox in a timeframe'
+    task cleanup_orphan_conversations: :environment do
+      print 'Enter Account ID: '
+      account_id = $stdin.gets.to_i
+      account = Account.find(account_id)
+
+      print 'Enter timeframe in days (default: 7): '
+      days_input = $stdin.gets.strip
+      days = days_input.empty? ? 7 : days_input.to_i
+
+      # Build a common base relation with identical joins for OR compatibility
+      base = account
+             .conversations
+             .where('conversations.created_at > ?', days.days.ago)
+             .left_outer_joins(:contact, :inbox)
+
+      # Find conversations whose associated contact or inbox record is missing
+      conversations = base.where(contacts: { id: nil }).or(base.where(inboxes: { id: nil }))
+
+      count = conversations.count
+      puts "Found #{count} conversations without a valid contact or inbox."
+
+      if count.positive?
+        print 'Do you want to delete these conversations? (y/N): '
+        confirm = $stdin.gets.strip.downcase
+        if %w[y yes].include?(confirm)
+          conversations.destroy_all
+          puts 'Conversations deleted.'
+        else
+          puts 'No conversations were deleted.'
+        end
+      end
+    end
+  end
+end