Add flagship Become a Member page with interactive multi-step form

New trilingual /<lang>/become-a-member/ conversion page: hero with real-photo collage, why-join benefits, animated MSOS-in-numbers, ways to participate, membership-in-real-life and projects showcase (real project photos), testimonials, who-can-join, an adaptive multi-step form (student + supporter flows, conditional fields, progress, personalised messages, validation, success screen), FAQ and final CTA. Site-wide 'Become a member' buttons now link here. Form posts to a Google Form once wired; metrics/testimonials are placeholders to confirm.

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

mk/index.html

@@ -71,7 +71,7 @@
                 </ul>
             </nav>
             <div class="navigation-actions">
-                <button class="btn btn-secondary">Стани член</button>
+                <a href="../mk/become-a-member/" class="btn btn-secondary">Стани член</a>
                 <button class="btn btn-primary">Донирај</button>
                 <div class="language-selector">
                     <div class="current-lang">
@@ -141,7 +141,7 @@
         </ul>
     </nav>
     <div class="navigation-actions">
-        <button class="btn btn-secondary">Стани член</button>
+        <a href="../mk/become-a-member/" class="btn btn-secondary">Стани член</a>
         <button class="btn btn-primary">Донирај</button>
         <div class="language-selector">
             <button class="current-lang" id="mobile-lang-trigger">
@@ -186,7 +186,7 @@
                     <h1>Ги зајакнуваме младите со вештини за да го променат светот</h1>
                     <p>Без разлика дали имате тим од 2 или 200 луѓе, нашите заеднички тимски сандачиња ги одржуваат сите на иста страна и во тек со случувањата.</p>
                 </div>
-                <button class="btn btn-primary-orange">Стани член</button>
+                <a href="../mk/become-a-member/" class="btn btn-primary-orange">Стани член</a>
             </div>
         </section>
 
@@ -252,7 +252,7 @@
                         <li>Забава и дружење</li>
                         <li>Студентска поддршка</li>
                     </ul>
-                    <button class="btn btn-primary-orange">Стани член</button>
+                    <a href="../mk/become-a-member/" class="btn btn-primary-orange">Стани член</a>
                 </div>
                 <div class="activity-details">
                     <p>Sed molestie penatibus sit bibendum pharetra purus faucibus fames aliquet. Morbi morbi ac sed tempor porta. Dui iaculis vitae fames sapien. Pellentesque urna eget habitasse arcu sed ornare. Dignissim lobortis ultrices maecenas magna ac habitant donec etiam at.</p>