Link "Become a member" CTAs directly to the signup form

Every body CTA (hero buttons, join-cta sections, article sidebars,
activities CTA) now points to become-a-member/#join-form so a click
lands on the form instead of the top of the page. The header menu
tab (btn-secondary) is intentionally left pointing at the page root.

93 links across 45 pages (en/mk/si). HTML-only, self-templated build
preserves the sidebar CTAs, so no rebuild/cache-bust needed.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

en/index.html

@@ -208,7 +208,7 @@
                     <h1>Empowering young people with skills to change the world</h1>
                     <p>Be part of our exciting journey; Become a part of our student organization today!</p>
                 </div>
-                <a href="../en/become-a-member/" class="btn btn-primary-orange">Become a member</a>
+                <a href="../en/become-a-member/#join-form" class="btn btn-primary-orange">Become a member</a>
             </div>
         </section>
 
@@ -295,7 +295,7 @@
                         <span class="activity-tab-label">Student Representation</span>
                     </button>
                     </div>
-                    <a href="../en/become-a-member/" class="btn btn-primary-orange activities-cta">Become a member</a>
+                    <a href="../en/become-a-member/#join-form" class="btn btn-primary-orange activities-cta">Become a member</a>
                 </div>
                 <div class="activities-panels">
                 <div class="activity-panel active" role="tabpanel" data-panel="0">
@@ -414,7 +414,7 @@
                 <h2>Find your people in Slovenia</h2>
                 <p class="join-cta-lead">Meet people, join events, get support, create projects and become part of the Macedonian student community across Slovenia.</p>
                 <div class="join-cta-actions">
-                    <a class="btn btn-primary-orange" href="../en/become-a-member/">Become a member</a>
+                    <a class="btn btn-primary-orange" href="../en/become-a-member/#join-form">Become a member</a>
                     <a class="btn btn-secondary" href="../en/projects/">See what we do</a>
                 </div>
             </div>