Fix broken action buttons and add delete confirmation modal

- shares.js, users.js: JSON.stringify() inside onclick="..." attributes
  produced unescaped " chars that broke HTML attribute parsing — all
  dynamic onclick JSON now passed through esc() so the browser decodes
  " back to " before executing the handler
- Replace browser confirm() dialogs with a styled Bootstrap modal
  (#deleteModal) for share and user deletion — reusable across all tabs
- users.js: rename shadow variable 'confirm' → 'pwConfirm' to avoid
  shadowing the now-removed confirm() call
- main.js: auto-refresh now reloads shares and users every 30 s,
  not just the dashboard

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

templates/index.html

@@ -65,6 +65,25 @@
     </div>
 </div>
 
+<!-- Delete confirm modal -->
+<div class="modal fade" id="deleteModal" tabindex="-1">
+    <div class="modal-dialog modal-sm">
+        <div class="modal-content">
+            <div class="modal-header border-0 pb-0">
+                <h5 class="modal-title" style="color:var(--red)">Delete</h5>
+                <button type="button" class="btn-close btn-close-white" data-bs-dismiss="modal"></button>
+            </div>
+            <div class="modal-body pt-2">
+                <p id="deleteModalMsg" class="mb-0" style="color:var(--muted)"></p>
+            </div>
+            <div class="modal-footer border-0 pt-0">
+                <button type="button" class="btn btn-secondary btn-sm" data-bs-dismiss="modal">Cancel</button>
+                <button type="button" class="btn btn-danger btn-sm" id="deleteModalConfirm">Delete</button>
+            </div>
+        </div>
+    </div>
+</div>
+
 <!-- Header -->
 <div class="topbar d-flex justify-content-between align-items-center">
     <span class="fw-semibold fs-5">MicroNAS</span>