feat(phase4e): batch delete with multi-select

- KeyList: multi-select mode with checkbox toggle
- Batch delete bar shows selected count + delete button
- RedisService: batchDelete using pipeline
- Preload: batchDelete IPC channel

src/preload/index.ts

@@ -92,6 +92,8 @@ const electronAPI = {
     // Memory
     memoryUsage: (id: string, key: string): Promise<number | null> =>
       ipcRenderer.invoke('redis:memoryUsage', id, key),
+    batchDelete: (id: string, keys: string[]): Promise<number> =>
+      ipcRenderer.invoke('redis:batchDelete', id, keys),
   },
 }