feat(auth): implement authentication system foundation

Add user authentication infrastructure with login/logout functionality,
session management, and basic user model.

Changes:
- Create users table with email, password_digest, confirmation tokens
- Add Users repository with authentication methods
- Add User entity with authentication helpers
- Implement login form and authentication actions
- Add logout action
- Add BCrypt gem for password hashing
- Update base Action class with authentication helpers
- Add login/logout routes

Next steps: Registration flow, password reset, email confirmation

app/actions/auth/logout.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+module EuchreCamp
+  module Actions
+    module Auth
+      class Logout < EuchreCamp::Action
+        def handle(request, response)
+          request.session.clear
+          response.redirect_to '/rankings'
+        end
+      end
+    end
+  end
+end