plex: add env vars (PLEX_UID/GID, TZ, ALLOWED_NETWORKS); homepage: rename Overseerr->Seerr

Plex Deployment had no Plex env vars. Add via the ServiceDefinition env list
(rendered verbatim by catalog/render.py):
- PLEX_UID/PLEX_GID=1000 (image chowns /config to this and drops; matches the
  Longhorn ownership convention seerr/semaphore use)
- TZ=Etc/UTC (no other service sets TZ repo-wide)
- ALLOWED_NETWORKS=10.0.0.0/8,192.168.0.0/16 so in-cluster clients (Seerr ->
  plex:32400) are trusted as LAN (pod CIDR 10.0.0.0/16 + svc 10.43.0.0/16 + LAN)

PLEX_CLAIM intentionally not set (4-min TTL is unusable via git; one-time live
claim persists on /config). ADVERTISE_IP deferred: the only candidate host
resolves via split-horizon DNS to the internal Gateway VIP and its remote
reachability is unverified — a wrong value breaks remote access, so omitted
per prefer-safety, documented as a follow-up in catalog/plex.yaml.

Homepage still labeled seerr as "Overseerr"; renamed the tile to "Seerr"
(icon mdi-play-box-multiple keeps — not overseerr-specific).

Co-Authored-By: Claude Opus 4.8 <[email protected]>

platform/homepage/configmap.yaml

@@ -61,7 +61,7 @@ data:
             href: https://plex.home.keithjackson.dev
             description: Media streaming
             icon: mdi-plex
-        - Overseerr:
+        - Seerr:
             href: https://seerr.home.keithjackson.dev
             description: Media requests
             icon: mdi-play-box-multiple