PDF: undo delete pages (30 sec window)

- Undo button appears after deleting pages
- Restores original file with all pages
- Re-renders all grids with restored pages
- Auto-hides after 30 seconds

public/pdf.html

@@ -769,6 +769,7 @@
                     <div class="page-grid" id="deletePageGrid"></div>
                     <div class="grid-action-bar">
                         <button class="grid-action-btn danger" id="btnDeleteSelected" disabled onclick="executeDeletePages()">Удалить выбранные (<span id="deleteCount">0</span>)</button>
+                        <button class="grid-action-btn" id="btnUndoDelete" style="display:none;background:var(--surface-600);color:var(--text-secondary);" onclick="undoDeletePages()">Отменить</button>
                         <span class="page-grid-hint" id="deleteHint"></span>
                     </div>
                 </div>
@@ -1824,6 +1825,9 @@
             return;
         }
         clearError();
+        // Save backup for undo
+        const backupFile = { ...selFile };
+        _deleteBackup = { file: backupFile };
         // Hide deleted pages visually
         const grid = document.getElementById('deletePageGrid');
         if (grid) {
@@ -1843,7 +1847,14 @@
             await syncAfterOperation(data);
         } catch(e) { showError(e.message); }
         document.getElementById('btnDeleteSelected').textContent = 'Удалить выбранные (0)';
+        document.getElementById('btnUndoDelete').style.display = '';
         updateDeleteCount();
+        // Auto-hide undo after 30 seconds
+        setTimeout(() => {
+            _deleteBackup = null;
+            var ub = document.getElementById('btnUndoDelete');
+            if (ub) ub.style.display = 'none';
+        }, 30000);
     };
 
     window.executeRotatePages = async function() {
@@ -2025,6 +2036,23 @@
         });
     }
 
+
+    // ─── Undo delete ──────────────────────────────────────────────────────────
+    let _deleteBackup = null; // { fileId, file object before delete }
+
+    window.undoDeletePages = function() {
+        if (!_deleteBackup) return;
+        // Restore the backed-up file
+        const old = _deleteBackup;
+        state.files = state.files.map(f => f.id === state.selectedFileId ? old.file : f);
+        state.selectedFileId = old.file.id;
+        _deleteBackup = null;
+        document.getElementById('btnUndoDelete').style.display = 'none';
+        stepResult.style.display = 'none';
+        downloadLink.style.display = 'none';
+        renderFileList();
+    };
+
 })();
 
 </script>