fix: dropdown strategy=fixed pour échapper au overflow du tableau

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

web/index.php

@@ -43,7 +43,7 @@ html_navbar('mail');
     </div>
 
     <div class="card shadow-sm" id="mail-card">
-        <div class="table-responsive" style="overflow:visible">
+        <div class="table-responsive">
             <table class="table table-hover align-middle mb-0">
                 <thead class="table-light">
                     <tr>
@@ -102,7 +102,7 @@ function buildTransferDropdown(sourceId, currentUsername) {
         </a></li>`
     ).join('');
     return `<div class="btn-group">
-        <button class="btn btn-sm btn-outline-primary dropdown-toggle" data-bs-toggle="dropdown" data-bs-boundary="viewport" title="Transférer vers…">
+        <button class="btn btn-sm btn-outline-primary dropdown-toggle" data-bs-toggle="dropdown" data-bs-strategy="fixed" title="Transférer vers…">
             <i class="bi bi-share"></i>
         </button>
         <ul class="dropdown-menu dropdown-menu-end shadow">${items}</ul>