feat: Spring Boot backend with deploy pipeline

- REST API: POST/GET/DELETE /api/apps
- Build pipeline: JAR → Dockerfile → docker build → push → kubectl apply
- In-memory state with K8s reconciliation on startup
- Shell executor for docker/kubectl commands
- Configurable via env vars (server URL, bootstrap token, registry, namespace)

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

target/classes/application.yml

@@ -0,0 +1,17 @@
+server:
+  port: 8082
+
+spring:
+  servlet:
+    multipart:
+      max-file-size: 200MB
+      max-request-size: 200MB
+
+cameleer:
+  deploy:
+    server-url: ${CAMELEER_SERVER_URL:http://cameleer3-server.cameleer.svc:8081}
+    bootstrap-token: ${CAMELEER_BOOTSTRAP_TOKEN:changeme}
+    registry: ${CAMELEER_REGISTRY:gitea.siegeln.net/cameleer/demo-apps}
+    agent-maven-url: ${CAMELEER_AGENT_MAVEN_URL:https://gitea.siegeln.net/api/packages/cameleer/maven/com/cameleer3/cameleer3-agent/1.0-SNAPSHOT/cameleer3-agent-1.0-SNAPSHOT.jar}
+    demo-namespace: ${CAMELEER_DEMO_NAMESPACE:cameleer-demo}
+    cameleer-server-ui: ${CAMELEER_SERVER_UI:http://localhost:8081}