Extract pages into lib/page/ modules; thin down bbs.rb

Each page is now a self-contained module with a configure(tui) class
method. Shared helpers live in TUIHelpers. bbs.rb is reduced to
constants, chrome, and wiring.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/page/idle_page.rb

@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+module IdlePage
+  def self.configure(tui)
+    tui.page :idle do
+      enter { @page_title = 'TELETYPE BBS' }
+
+      render do
+        text 'Navigate the menu with ↑↓, select with Enter.',
+             x: CONT_X, y: CONT_Y + cont_h / 2, style: THEME[:normal]
+      end
+
+      nav :menu, size: MENU_ITEMS.size
+      key(:enter) do
+        case MENU_ITEMS[@menu_sel]
+        when 'Messages'     then go :messages
+        when 'Post Message' then go :new_msg
+        when 'Blog Posts'   then go :blog
+        when 'HowTo Guides' then go :howto
+        when 'Game Catalog' then go :games
+        when 'Online Users' then go :online
+        when 'System Info'  then go :sysinfo
+        when 'Exit'         then :halt
+        end
+      end
+      key('q')     { :halt }
+      key(:escape) { :halt }
+    end
+  end
+end