Fix container name handling for hyphenated service names

Extract ContainerNameFor and SplitContainerName into names.go.
ContainerNameFor handles single-component services where service
name equals component name (e.g., mc-proxy → "mc-proxy" not
"mc-proxy-mc-proxy"). SplitContainerName checks known services
from the registry before falling back to naive split on "-", fixing
mc-proxy being misidentified as service "mc" component "proxy".

Also fixes podman ps JSON parsing (Command field is []string not
string) found during deployment.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/systemd/mcp-agent.service

@@ -11,6 +11,8 @@ RestartSec=5
 
 User=mcp
 Group=mcp
+Environment=HOME=/srv/mcp
+Environment=XDG_RUNTIME_DIR=/run/user/%U
 
 NoNewPrivileges=true
 ProtectSystem=strict