fix(node-agent): mount host SSH key into container for event shipping

Nodes ship events to VPS via rsync+SSH. The container runs as root
and uses the default SSH identity, which must be at /root/.ssh/.
Mount /home/oskar/.ssh from the host read-only so the existing
authorized key is available inside the container.

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

hosts/chelsty-infra/runtime/node-agent/docker-compose.override.yml

@@ -7,3 +7,5 @@ services:
       - VPS_EVENTS_USER=oskar
       - VPS_EVENTS_PATH=/opt/homelab/events
       - CHECK_INTERVAL=60
+    volumes:
+      - /home/oskar/.ssh:/root/.ssh:ro

hosts/piha/runtime/node-agent/docker-compose.override.yml

@@ -7,3 +7,5 @@ services:
       - VPS_EVENTS_USER=oskar
       - VPS_EVENTS_PATH=/opt/homelab/events
       - CHECK_INTERVAL=60
+    volumes:
+      - /home/oskar/.ssh:/root/.ssh:ro

hosts/solaria/runtime/node-agent/docker-compose.override.yml

@@ -7,3 +7,5 @@ services:
       - VPS_EVENTS_USER=oskar
       - VPS_EVENTS_PATH=/opt/homelab/events
       - CHECK_INTERVAL=60
+    volumes:
+      - /home/oskar/.ssh:/root/.ssh:ro