fix: resolve per-torrent qb save paths

docs/deployment-and-usage.md

@@ -120,6 +120,8 @@ username = "${QB_USER}"
 password_file = "/run/secrets/qb_password"
 api_root = "/downloads"
 local_root = "/data/qb"
+# Optional only when a nested qB path uses a different client-visible mount.
+# local_path_overrides = { "/downloads/fast" = "/data/qb-fast" }
 
 [syncthing]
 endpoint = "http://syncthing:8384"
@@ -139,6 +141,14 @@ accounting. The override key is the normalized Syncthing folder path beneath
 `api_root`, not its folder ID. See the production deployment README for the
 required compose and override pattern.
 
+qBittorrent content is resolved differently: every existing torrent keeps its
+qB-reported `save_path`. The client maps that path beneath `qbittorrent.api_root`
+to its own mount before a source, existing-target, permission, or eviction
+operation. Thus `/downloads/Downloading` naturally maps below `/data/qb`;
+there is no migration or per-resource configuration. Add a qB
+`local_path_overrides` entry only when that nested API prefix is a separate
+client mount.
+
 The remaining node examples omit optional `[connection]`, `[jobs]`, and
 `[backup]` tables and therefore use these same defaults; deployments may
 override them per node.