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/sysinfo_page.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module SysinfoPage
+  def self.configure(tui)
+    tui.page :sysinfo do
+      enter do
+        @page_title = 'SYSTEM INFO'
+        @items = [
+          "Online users  #{ONLINE.count}",
+          "Messages      #{MESSAGES.count}",
+          "Wiki          https://wiki.teletypegames.org",
+          "Games API     https://teletypegames.org",
+          "Platform      #{RUBY_PLATFORM}",
+          "Ruby          #{RUBY_VERSION}"
+        ]
+      end
+
+      render do
+        @items.each_with_index do |row, i|
+          text row[0, cont_w], x: CONT_X, y: CONT_Y + i, style: THEME[:normal]
+        end
+        text 'q back', x: CONT_X, y: CONT_Y + cont_h, style: THEME[:normal]
+      end
+
+      key('q')     { go :idle }
+      key(:escape) { go :idle }
+    end
+  end
+end