stemd: AUTO_SCAN=0 runs on request only (Stem Now)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/README.md

@@ -129,6 +129,7 @@ the app would briefly see no stems.
 | `MODEL`      | `roformer_bs_sw` | any id from `stemify/catalog.py`                  |
 | `DEVICE`     | `cuda`           | `cuda`, `cuda:N` or `cpu`                            |
 | `RESCAN_MIN` | `30`             | minutes between scans once caught up                 |
+| `AUTO_SCAN`  | `1`              | `0` = never scan the library, only do Stem Now requests |
 | `FP16`       | `1`              | half precision on the GPU (`0` for fp32)             |
 | `OVERLAP`, `SEGMENT`, `SHIFTS` | `0.25`, `0`, `0` | as in the desktop app's settings     |