feat: modernize application — source, platform artifacts, CI/CD

- chore: ingest source code

108 files from https://github.com/spring-projects/spring-petclinic
- feat: add platform deployment artifacts
- feat: add CI/CD workflow automation

docs/api.md

@@ -0,0 +1,25 @@
+# API Reference
+
+## Endpoints
+
+### Health Check
+
+```
+GET /health
+```
+
+**Response:**
+```json
+{"status": "UP", "service": "demo-de-123"}
+```
+
+### Root
+
+```
+GET /
+```
+
+**Response:**
+```json
+{"service": "demo-de-123", "description": "Modernized demo-de-123 service", "version": "1.0.0"}
+```