fix: add periodic cleanup of login_attempts hash

Sweep stale entries every 5 minutes to prevent unbounded memory growth
from IPs that touch the login endpoint once and never return.

lib/volumen.rb

@@ -18,11 +18,24 @@ require_relative "volumen/users"
 # The Sinatra app (`Volumen::Server`) and the CLI (`Volumen::CLI`) are loaded
 # on demand to keep the core library light.
 module Volumen
+  CLEANUP_INTERVAL = 300 # seconds between full sweeps of login_attempts
+
   def self.login_attempts
     @login_attempts ||= {}
   end
 
   def self.reset_login_attempts!
     @login_attempts = {}
+    @last_cleanup = nil
+  end
+
+  def self.sweep_login_attempts!
+    now = Time.now.to_f
+    return if @last_cleanup && (now - @last_cleanup) < CLEANUP_INTERVAL
+
+    cutoff = now - Volumen::Server::LOGIN_WINDOW
+    login_attempts.each_value { |timestamps| timestamps.select! { |t| t > cutoff } }
+    login_attempts.delete_if { |_ip, timestamps| timestamps.empty? }
+    @last_cleanup = now
   end
 end

lib/volumen/server.rb

@@ -224,6 +224,7 @@ module Volumen
     end
 
     def check_login_rate_limit!
+      Volumen.sweep_login_attempts!
       ip = request.ip.to_s
       now = Time.now.to_f
       cutoff = now - LOGIN_WINDOW

test/admin_test.rb

@@ -221,6 +221,14 @@ class AdminTest < Minitest::Test
     assert File.exist?(File.join(@posts_dir, "by-author.md"))
   end
 
+  def test_login_rate_limit_sweep_removes_stale_entries
+    Volumen.login_attempts["1.2.3.4"] = [Time.now.to_f - 120]
+    Volumen.instance_variable_set(:@last_cleanup, Time.now.to_f - 600)
+    Volumen.sweep_login_attempts!
+    refute Volumen.login_attempts.key?("1.2.3.4"),
+           "sweep should remove IPs with only stale entries"
+  end
+
   private
 
   def csrf(body)