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/login.rb

@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+module EuchreCamp
+  module Actions
+    module Auth
+      class Login < EuchreCamp::Action
+        include Deps[
+          users_repo: 'repositories.users',
+          players_repo: 'repositories.players'
+        ]
+
+        # Show login form (GET)
+        class Show < Login
+          def handle(request, response)
+            render_with_player(request, response)
+          end
+        end
+
+        # Process login (POST)
+        class Create < Login
+          def handle(request, response)
+            email = request.params[:email]
+            password = request.params[:password]
+
+            user = users_repo.by_email(email)
+
+            if user && valid_password?(user, password)
+              if user.locked?
+                response.flash[:error] = 'Account is locked. Please contact support.'
+                response.redirect_to '/login'
+                return
+              end
+
+              # Record successful login
+              ip_address = request.env['REMOTE_ADDR']
+              users_repo.record_login(user[:id], ip_address)
+
+              # Create session
+              session = request.session
+              session[:user_id] = user[:id]
+              session[:player_id] = user[:player_id]
+
+              response.flash[:success] = 'Welcome back!'
+              response.redirect_to '/rankings'
+            else
+              # Record failed login
+              users_repo.record_failed_login(user[:id]) if user
+
+              response.flash[:error] = 'Invalid email or password'
+              response.redirect_to '/login'
+            end
+          end
+
+          private
+
+          def valid_password?(user, password)
+            BCrypt::Password.new(user[:password_digest]) == password
+          end
+        end
+      end
+    end
+  end
+end