fix(demo): resolve duplicate deploy key and env var bootstrapping

- Remove duplicate `deploy:` block in atomictracker service that
  caused YAML parse failure on docker compose up
- Fix yamllint errors: wrap long lines in socket proxy label and
  Elasticsearch health check
- Add MAILHOG_SMTP_PORT migration to ensure_env() so older demo.env
  files get the new variable appended automatically
- Verified: full stack deploys, 91/91 tests pass (52 unit + 39 e2e),
  all 16 services healthy, 13/13 smoke ports accessible

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

demo/docker-compose.yml.template

@@ -79,7 +79,8 @@ services:
       homepage.group: "Infrastructure"
       homepage.name: "Docker Socket Proxy"
       homepage.icon: "docker"
-      homepage.description: "Secure proxy for Docker socket access (internal only)"
+      homepage.description: >-
+        Secure proxy for Docker socket access (internal only)
 
   # Homepage - Central Dashboard
   homepage:
@@ -343,10 +344,6 @@ services:
       resources:
         limits:
           memory: 256M
-    deploy:
-      resources:
-        limits:
-          memory: 256M
     healthcheck:
       test: ["CMD", "wget", "--no-verbose", "--tries=1", "--spider",
              "http://localhost:8080"]
@@ -437,7 +434,9 @@ services:
         limits:
           memory: 1024M
     healthcheck:
-      test: ["CMD-SHELL", "curl -sf http://localhost:9200/_cluster/health || exit 1"]
+      test:
+        ["CMD-SHELL",
+         "curl -sf http://localhost:9200/_cluster/health || exit 1"]
       interval: ${HEALTH_CHECK_INTERVAL}
       timeout: ${HEALTH_CHECK_TIMEOUT}
       retries: 10