chore: remove dead machine-level Jellyfin/Jellyseerr fields

Follow-up #1 to the service-registry change. Jellyfin/Jellyseerr now resolve
from the service registry, so the machine-level app fields are dead config.

- dependencies.py: drop dead _jellyseerr_client_for; simplify _resolve_machine
  to SSH-only.
- settings_store.py + routers/settings.py: remove jellyfin_*/jellyseerr_* from
  machine default config, get_machine_config, normalization, row mappers, and
  MachineInput.
- frontend types + Settings.tsx: drop the fields and the Jellyfin/Jellyseerr
  form sections + service options.
- Update frontend test fixtures.

Existing DB rows may still carry these keys in config_json; they are inert and
drop on the next machine save. Verification: backend ruff clean, pytest 222;
frontend lint 0 errors, build success, 70 tests.

CHANGELOG.md

@@ -54,3 +54,13 @@ All notable changes to Manage. Breaking changes are marked with **BREAKING**.
 - Machine-level Jellyfin/Jellyseerr app config still powers the Media/Users/Files
   pages. Migrating those onto the service registry is a separate follow-up change
   (see `openspec/changes/service-registry/design.md` §12.5).
+
+## Follow-up #1 — remove dead machine Jellyfin/Jellyseerr fields
+
+With Jellyfin/Jellyseerr now resolved from the service registry, the machine-level
+Jellyfin/Jellyseerr fields are dead config. Removed from `dependencies.py` (dead
+`_jellyseerr_client_for`; `_resolve_machine` simplified to SSH-only),
+`services/settings_store.py`, `routers/settings.py` (`MachineInput`), frontend
+types, the `Settings.tsx` form, and frontend test fixtures. Existing DB rows may
+still carry these keys in `config_json`; they are inert and get dropped on the
+next machine save. No data migration required.