Fix double main tag nesting and mission/vision CSS selector conflicts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: congwang-mk

_layouts/default.html

@@ -326,9 +326,7 @@
         </div>
     </header>
 
-    <main>
-        {{ content }}
-    </main>
+    {{ content }}
 
     <!-- Enterprise-grade footer -->
     <footer class="enterprise-footer">