homepage: function-first layout + fleet label sweep

Reorganize the gethomepage dashboard from site-based (PFI-ANA, ESH, NH3)
to function-first grouping (Monitoring, AI Systems, Apps, Media, Games,
Infra-<site>, Service Networking). Canonical config now tracked in
configs/homepage/ with Plex/Jellyfin widget keys moved to env
substitution.

Label sweep across fleet compose files:
  - beszel, dozzle, backrest -> Monitoring
  - rest-server-ana -> Service Networking

Healthcheck fixes (previous wget/curl paths broke on distroless +
--private-repos 401):
  - beszel hub:    /beszel health --url ...
  - beszel agent:  /agent health (newly added)
  - rest-server:   nc -z localhost 8000 (TCP probe)

Group name originally "Wiring / Plumbing" collapsed to single-word group
on homepage's parser; renamed to "Service Networking" everywhere.

stacks/rest-server-nh3/compose.yaml

@@ -33,7 +33,9 @@ services:
     # automatically — no extra bind mount needed as long as the htpasswd
     # file is created inside DATA_DIR before startup.
     healthcheck:
-      test: ["CMD-SHELL", "wget -qO- http://localhost:8000/metrics >/dev/null || exit 1"]
+      # TCP port probe — avoids the --private-repos 401 trap.
+      # See stacks/rest-server-ana/compose.yaml for reasoning.
+      test: ["CMD", "nc", "-z", "localhost", "8000"]
       interval: 30s
       timeout: 10s
       retries: 3