Account namespace updates: part 4 (transfers, singular namespacing) (#896)

* Move Transfer to Account namespace

* Fix partial resolution due to namespacing plurality

* Make category and tag controllers consistent with namespacing convention

* Update stale partial reference

db/migrate/20240620125026_rename_transfer_table.rb

@@ -0,0 +1,5 @@
+class RenameTransferTable < ActiveRecord::Migration[7.2]
+  def change
+    rename_table :transfers, :account_transfers
+  end
+end