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/messages_page.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module MessagesPage
+  def self.configure(tui)
+    tui.page :messages do
+      enter do
+        @page_title = 'MESSAGES'
+        @items  = MESSAGES.last(30).map { |m| "#{tc(:label, m.timestamp)} #{tc(:bright, m.username)}: #{m.text}" }
+        @scroll = 0
+      end
+
+      render do
+        (@items[@scroll, cont_h] || []).each_with_index do |line, i|
+          text line[0, cont_w], x: CONT_X, y: CONT_Y + i
+        end
+        text "#{@items.size} msg(s)  ↑↓ scroll  q back",
+             x: CONT_X, y: CONT_Y + cont_h, style: THEME[:normal]
+      end
+
+      nav :scroll, content: -> { @items }, window: -> { cont_h }
+      key('r')     { reload }
+      key('q')     { go :idle }
+      key(:escape) { go :idle }
+    end
+  end
+end