refactor(demo): replace Portainer with Dockhand

Replace Portainer container management service with Dockhand:
- Update docker-compose.yml.template with Dockhand service definition
- Replace portainer_data volume with dockhand_data
- Update PORTAINER_PORT to DOCKHAND_PORT in demo.env
- Update all script references (demo-stack.sh, demo-test.sh, validate-all.sh)
- Update integration test from Portainer to Dockhand
- Update documentation files (README.md, AGENTS.md, api-docs,
  service-guides, troubleshooting)

Dockhand provides modern Docker management UI with:
- Container lifecycle management
- Compose stack orchestration
- Git-based deployments
- Multi-environment support
- Terminal access and log streaming
- File browser capabilities

Maintains same port (4007) for consistency.

💘 Generated with Crush

Assisted-by: GLM-4.7 via Crush <crush@charm.land>

demo/tests/integration/test_service_communication.sh

@@ -15,13 +15,13 @@ test_grafana_influxdb_integration() {
     fi
 }
 
-test_portainer_docker_integration() {
-    # Test Portainer can reach Docker socket
-    if docker exec tsysdevstack-supportstack-demo-portainer docker version >/dev/null 2>&1; then
-        echo "PASS: Portainer-Docker integration"
+test_dockhand_docker_integration() {
+    # Test Dockhand can reach Docker socket
+    if docker exec tsysdevstack-supportstack-demo-dockhand docker version >/dev/null 2>&1; then
+        echo "PASS: Dockhand-Docker integration"
         return 0
     else
-        echo "FAIL: Portainer-Docker integration"
+        echo "FAIL: Dockhand-Docker integration"
         return 1
     fi
 }
@@ -41,5 +41,5 @@ test_homepage_discovery() {
 
 # Run integration tests
 test_grafana_influxdb_integration
-test_portainer_docker_integration
+test_dockhand_docker_integration
 test_homepage_discovery