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/wiki_list_page.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module WikiListPage
+  def self.configure(tui, name, category:, title:)
+    tui.page name do
+      enter do
+        @page_title = title
+        @items      = WIKI.list(category)
+        @item_sel   = 0
+        @scroll     = 0
+      end
+
+      render { wiki_list_render }
+
+      nav :list, window: -> { cont_h - 3 }
+      key(:enter)  { open_wiki_page(back: name) }
+      key('r')     { reload }
+      key('q')     { go :idle }
+      key(:escape) { go :idle }
+    end
+  end
+end