4K: download clients (packaged, idempotent) + Homepage tiles

Add SABnzbd+Transmission to radarr-4k/sonarr-4k with distinct categories (sabnzbd
movies-4k/tv-4k, transmission radarr-uhd/sonarr-uhd; Transmission forbids digits) so
they dont cross-import the 1080p instances. Packaged into deploy-arrs-4k.yml via an
idempotent ensure-arrs-4k-dl.py (changed=0). Homepage Radarr 4K/Sonarr 4K tiles
(HOMEPAGE_VAR keys, siteMonitor). 4K path proven: Obsession routed to radarr-4k,
grabbed WEBDL-2160p, 1080p rejected 'not wanted in profile'. Keys via vault, no secrets.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

arrs-4k/README.md

@@ -21,6 +21,11 @@ idempotent, changed=0).
   1080p radarr was mislabeled `is4k=true` and was flipped to `is4k=false` (non-4k default).
 - **Plex**: SEPARATE libraries `Movies - 4K` (/data/media/movies-4k) + `TV - 4K` (/data/media/tv-4k),
   not merged into the 1080p libraries.
+- **Download clients** (added post-Step-1, packaged in the playbook via `ensure-arrs-4k-dl.py`):
+  SABnzbd + Transmission on both instances, DISTINCT categories to avoid cross-import with 1080p —
+  sabnzbd `movies-4k`/`tv-4k`, transmission `radarr-uhd`/`sonarr-uhd` (Transmission category forbids digits).
+  Completed paths under /data (hardlinks intact).
+- **Homepage**: separate `Radarr 4K`/`Sonarr 4K` tiles in Media Automation (keys via HOMEPAGE_VAR, siteMonitor).
 - **Traefik**: file-provider routers (see traefik-router snippet), NOT docker labels.
 - **Tdarr**: does NOT watch movies-4k/tv-4k (its libraries are the specific 1080p /media/movies,
   /media/tv) — quality-first keeps the grabbed file.