Add billing system with Stripe

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Jason Zimdars <jz@37signals.com>

test/models/card_test.rb

@@ -81,7 +81,7 @@ class CardTest < ActiveSupport::TestCase
 
   test "open" do
     assert_equal cards(:logo, :layout, :text, :buy_domain).to_set, accounts("37s").cards.open.to_set
-    assert_equal cards(:radio, :paycheck).to_set, accounts("initech").cards.open.to_set
+    assert_equal cards(:radio, :paycheck, :unfinished_thoughts).to_set, accounts("initech").cards.open.to_set
   end
 
   test "card_unassigned" do