fix: two observability bugs from initial deployment

Fix 1 - UnPoller 404 on UDM Pro:
  Remove :8443 from UP_UNIFI_DEFAULT_URL. UniFi OS devices (UDM Pro,
  UDM, UXG, CloudKey) use a different API path and do NOT use port 8443.
  URL should be https://10.42.1.1 (no port); unpoller handles the
  /proxy/network path internally for UniFi OS devices.

Fix 2 - Grafana dashboards showing invalid datasource:
  Add uid = "prometheus" to the provisioned Prometheus datasource.
  Without an explicit UID, Grafana auto-generates one on first run.
  All dashboard JSON references datasource uid "prometheus" which
  only works if the provisioning explicitly sets that UID.

hosts/unstable/hosea/default.nix

@@ -123,6 +123,7 @@ in
           {
             name = "Prometheus";
             type = "prometheus";
+            uid = "prometheus";
             url = "https://prometheus.shire-zebra.ts.net";
             isDefault = true;
             editable = false;