[recipe] Refactor recipe demo to use KV interfaces (Ascend#55)

### Summary

Offer a new single_controller_demo to use the high-level KV interface
(tq.init / tq.kv_batch_put / KVBatchMeta) instead of the low-level
native interface (TransferQueueController, SimpleStorageUnit,
process_zmq_server_info).

### Changes
- Retired legacy sync_demo.py and async_demo.py
- Replaced low-level controller/storage setup with tq.init(conf=config)
- Switched from BatchMeta-based flow to KVBatchMeta-based flow: put
prompts by UUID keys, sample global_batch_size keys via random.sample,
pass KVBatchMeta through worker functions

Author: dodatboii