feat(sprint-5): Phase 1 — Docker Compose full stack, CORS, Next.js upgrade

- Dockerfile.backend: multi-stage Java 21 build (eclipse-temurin)
- docker-compose.yml: PostgreSQL 16 + backend + frontend with health checks
- SecurityConfig: CORS for localhost:3000 frontend origin
- application-docker.properties: Docker profile with env vars
- Spring Boot Actuator health endpoint enabled
- Next.js upgraded 15.2.8 → 15.5.18 (security fixes)

cannamanage-frontend/package.json

@@ -46,7 +46,7 @@
     "emoji-picker-react": "4.12.2",
     "input-otp": "1.4.2",
     "lucide-react": "0.446.0",
-    "next": "15.2.8",
+    "next": "15.5.18",
     "next-auth": "5.0.0-beta.31",
     "next-intl": "^4.13.0",
     "react": "19.1.3",
@@ -72,7 +72,7 @@
     "@types/react": "19.0.12",
     "@types/react-dom": "19.0.4",
     "eslint": "9.18.0",
-    "eslint-config-next": "15.2.8",
+    "eslint-config-next": "15.5.18",
     "eslint-config-prettier": "10.1.1",
     "eslint-plugin-prettier": "5.2.3",
     "playwright": "^1.60.0",