Add transmission dashboard to grafana

- Add node_exporter ansible role to enable textfile collector
- Add transmission_metrics role with script and LaunchAgent
  - Collects metrics every 60s via transmission RPC
  - Writes to /opt/homebrew/var/node_exporter/textfile/transmission.prom
- Update grafana role to provision dashboards from files
- Add transmission.json dashboard with:
  - Status indicator, torrent counts
  - Transfer speeds, cumulative stats
  - Time series graphs

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ansible/playbooks/indri.yml

@@ -2,12 +2,16 @@
 - name: Configure indri
   hosts: indri
   roles:
+    - role: node_exporter
+      tags: node_exporter
     - role: prometheus
       tags: prometheus
     - role: grafana
       tags: grafana
     - role: transmission
       tags: transmission
+    - role: transmission_metrics
+      tags: transmission_metrics
     - role: kiwix
       tags: kiwix
     - role: borgmatic