Header 1.2: Resources Megamenu

Based on header-design-1-systemized.html. The Resources link now opens a full-width megamenu with two columns:

Col 1 — Browse by Type: Articles, Books, Series, Testimonies, News, Conferences, Regional Equips.
Col 2 — Topics: The Apostolic, Church Planting, Children, Youth, Women, Worship.
About & Partner retain the original single-column dropdown.
Smart Sticky & Mobile Drawer behaviour unchanged.

            <div class="nav-item nav-item--mega">

              <a class="nav-link">Resources</a>

              <div class="megamenu">

                <div class="megamenu-col">...types...</div>

                <div class="megamenu-col">...topics...</div>

              </div>

            </div>