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/main/ipc-handlers.ts

@@ -179,4 +179,7 @@ export function registerIpcHandlers(): void {
   ipcMain.handle('redis:memoryUsage', async (_e, id: string, key: string) => {
     return redisService.memoryUsage(id, key)
   })
+  ipcMain.handle('redis:batchDelete', async (_e, id: string, keys: string[]) => {
+    return redisService.batchDelete(id, keys)
+  })
 }