feat(ha-diag-agent): add piha deploy config

- hosts/piha/runtime/ha-diag-agent/docker-compose.override.yml: mem_limit
  128m, hardcoded events volume (/opt/homelab/events/piha:/events) to avoid
  ${NODE_NAME} shell-expansion issue in deploy-node.sh
- services/ha-diag-agent/env.example: per-host HA_URL comments (piha vs
  chelsty-infra tailscale), HA_TOKEN source note

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

hosts/piha/runtime/ha-diag-agent/docker-compose.override.yml

@@ -0,0 +1,10 @@
+services:
+  ha-diag-agent:
+    # Pin events to the piha-specific subdirectory; overrides the ${NODE_NAME}
+    # variable substitution in the base compose file which requires a shell env var.
+    volumes:
+      - /opt/homelab/events/piha:/events
+      - /var/lib/ha-diag-agent:/data
+      - /opt/homelab/config/ha-diag-agent:/config:ro
+    mem_limit: 128m
+    restart: unless-stopped

services/ha-diag-agent/env.example

@@ -2,11 +2,14 @@
 # Copy to /opt/homelab/config/ha-diag-agent/.env on the target node
 
 # Home Assistant connection (required)
-HA_URL=http://homeassistant.local:8123
+# piha:          HA_URL=http://localhost:8123
+# chelsty-infra: HA_URL=http://100.70.180.90:8123  (chelsty-ha Tailscale IP)
+HA_URL=http://localhost:8123
+# Obtain from HA UI: Settings → People → <diag_agent user> → Long-Lived Access Tokens
 HA_TOKEN=your-long-lived-token-here
 HA_TIMEOUT=10.0
 
-# Node identity
+# Node identity  (must match the node's canonical name in the homelab inventory)
 NODE_NAME=piha
 LOCATION_TAG=ken