feat: trade-pro skeleton theme package (Phase 2)

Fifth built-in theme: English-first international B2B skeleton registered
via manifest discovery, builds real sites end-to-end. pro.html derives
from industrial with lang=en, href-set value-comparison English fallback
nav (header + footer), sf-tp-* button classes and hard-coded #0b3d91
theme-color until the map entry lands. pages/ ships all 14 kinds; macro
library is an English passthrough copy pending the Phase 3 cms port.

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

themes/trade-pro/pages/article.html

@@ -0,0 +1 @@
+<section class="pro-article-hero"><div class="pro-wrap pro-article-width"><span class="pro-eyebrow">LATEST NEWS / INSIGHTS</span><h1>{{page.title}}</h1><p>{{page.summary}}</p>{% if fields.get('publish_date') %}<time>{{fields.get('publish_date')}}</time>{% endif %}</div></section><article class="pro-wrap pro-article-content">{% if page.cover %}<img class="pro-article-cover" src="{{safe_image(page.cover)}}" alt="{{page.title}}">{% endif %}{{body_copy(content,page)}}<a class="pro-text-link" href="/news/">← Back to news</a></article>