feat(jellyfin): the provider keys ride a host file the deployer installs

Jellyfin 12 ships TMDB, TVDB, StudioImages and MusicBrainz as core plugins:
no DLL, only a configuration file under the data root, so the keys have to
reach that XML from somewhere that is not git. They live in the fleet's
per-service env-file convention -- /home/dank/Containers/jellyfin/provider-keys
(TMDB_API_KEY=, TVDB_API_KEY=, optional TVDB_PIN=, mode 600) -- and
scripts/jellyfin-providers.sh plan|install|verify reads only that file, prints
no key byte, and refuses a keys file that is not mode 600 or that has no line
for the provider about to be written. install is idempotent: it never touches
a key the UI already saved, backs up every XML it edits into
~/.AGENTTRASH/<date>-jellyfin-providers/ first, and only installs the TVDB
plugin when the pinned official zip carries the plugin guid.

The deployer runs install BEFORE it restarts jellyfin, because the plugin and
its keys are read at start-up and a restart-first deploy boots the old state.
A missing keys file warns instead of failing: a host without the keys still
deploys, degraded rather than broken. No plugin configuration XML is tracked.

scripts/deploy-plan.py

@@ -476,6 +476,11 @@ def services_for_path(path: str, target: str) -> set[str]:
             # The installer is what creates, mounts and reaps the view both media
             # servers read, so a change to it is a restart of that pair.
             _add(services, "jellyfin", "plex")
+        if name == "jellyfin-providers.sh":
+            # The deployer runs this before jellyfin restarts, so a change to
+            # the installer is a change to the provider state Jellyfin loads at
+            # start-up: it selects jellyfin and nothing else.
+            _add(services, "jellyfin")
         if name in {"frank-zealot.env", "frank-zealot.service", "serve-frank-zealot.sh"}:
             # llama.cpp frank-zealot (2026-09-16) keeps its unit, env and serve
             # files here; each one selects frank-zealot only. The ik_llama.cpp