docs(media): how to file a below-threshold episode by hand

Six single-episode files stayed in the movie library when the threshold refused
them; the hand path is the same executor on a hand-written plan and the same
journal. The trap recorded here is the series year -- never inherit it from the
title whose bonus folder an episode happens to be parked in.

serverAppConfigs-docs/Dankserver/Jellyfin.md

@@ -42,6 +42,15 @@ public vhost `jelly.franksdank.cloud` behind the [[Anubis]] guard chain →
 Library folders point at `/data` paths; because the mount uses the same
 absolute path as on the host, library paths survive container recreation.
 
+`Local metadata` — save metadata to media folders — cannot work against a `ro`
+mount, and it is enabled: every item update logs
+`System.IO.IOException: Read-only file system : '/data/Movies/<film>/movie.nfo'`.
+The exception lands in the sidecar saver, after the database row is written, so
+indexing proceeds anyway — a 2026-10-30 scan dropped stale records and added
+episodes while these lines filled the log. Expected noise, not a fault: if it
+ever needs silencing, turn the saver off under *Library → Metadata* rather than
+making `/data` writable.
+
 ## Ports & access
 
 | Port | Proto | Purpose |