mem: reduce PaddleOCR rec_batch_num from 6 to 1
Paddle's native inference engine allocates 500 MiB memory arena chunks
during text recognition, proportional to batch size. With the default
rec_batch_num=6, four 500 MiB chunks are allocated simultaneously.
Setting rec_batch_num=1 reduces this to a single chunk, cutting peak
memory on the PaddleOCR code path by ~1,265 MiB (-42.6%).
Latency benchmark (55 text regions, CPU, 5 runs):
- rec_batch_num=6: 39.1s +/- 3.5s
- rec_batch_num=1: 37.0s +/- 2.0s
No throughput regression — on CPU, batch processing is sequential.
