manatee: Reload Plejd when its BLE link goes stale

pyplejd keeps using a dead BLE client ("Service Discovery has not been
performed yet") instead of reconnecting, which left the Plejd lights
unreachable for two days. Fire system log events and let an automation
reload the integration when that warning shows up.

Also add systemd to bt-reset's PATH so its `systemctl` calls work.

hosts/manatee/modules/home-assistant/default.nix

@@ -22,12 +22,35 @@ frontend:
   themes: !include_dir_merge_named themes
 
 automation: !include automations.yaml
+automation nix:
+  # pyplejd keeps using a dead BLE client forever ("Service Discovery has not
+  # been performed yet") instead of reconnecting; reloading the integration fixes it
+  - alias: Reload Plejd when its BLE link goes stale
+    mode: single
+    triggers:
+      - trigger: event
+        event_type: system_log_event
+        event_data:
+          level: WARNING
+    conditions:
+      - "{{ 'pyplejd' in trigger.event.data.name and 'Service Discovery has not been performed yet' in (trigger.event.data.message | join(' ')) }}"
+    actions:
+      - action: homeassistant.reload_config_entry
+        target:
+          entity_id: light.takbelysning
+      # With mode: single, this caps it at one reload per 5 minutes
+      - delay: "00:05:00"
+
 script: !include scripts.yaml
 scene: !include scenes.yaml
 
 recorder:
   purge_keep_days: 365
 
+# Turns logged warnings/errors into `system_log_event`s that automations can react to
+system_log:
+  fire_event: true
+
 alert:
   fridge_door:
     name: Fridge is open
@@ -64,6 +87,7 @@ ${cfg.extraConfig}'';
         pkgs.kmod
         pkgs.gnugrep
         pkgs.coreutils
+        pkgs.systemd
       ]
     }"