Add service_type field to separate data from presentation

Changes:
- Add service_type field to SubServiceData: 'nginx_site', 'container', 'image'
- Agent sends pure data without display formatting
- Dashboard checks service_type to decide presentation
- Docker images now display without status icon (service_type='image')
- Remove unused image_size_str from docker images tuple

Clean separation: agent provides data, dashboard handles display logic.

Cargo.lock

@@ -279,7 +279,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.188"
+version = "0.1.189"
 dependencies = [
  "anyhow",
  "chrono",
@@ -301,7 +301,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.188"
+version = "0.1.189"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -324,7 +324,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.188"
+version = "0.1.189"
 dependencies = [
  "chrono",
  "serde",