Refactor Drone CI and Dockerfile for optimized builds and runtime

Streamlined `.drone.yml` by removing redundant test-and-jar step, introducing image caching with `cache_from`, and refining conditional triggers. Enhanced `Dockerfile` with multi-stage builds for dependency warming, test execution, and efficient package creation, alongside runtime optimizations for graceful shutdown and resource management.

.drone.yml

@@ -6,13 +6,6 @@ environment:
   DOCKER_BUILDKIT: 1
 
 steps:
-  - name: test-and-jar
-    image: gradle:8.10.2-jdk21
-    # No host volumes; keep cache in the container layer only
-    commands:
-      - gradle --version
-      - gradle --no-daemon clean test bootJar
-
   - name: build-image
     image: plugins/docker
     settings:
@@ -27,11 +20,19 @@ steps:
         - ${DRONE_BRANCH/\//-}-${DRONE_COMMIT_SHA:0:7}
         - latest
       buildkit: true
+      # ⬇️ Pull last image and reuse its layers (huge win)
+      cache_from:
+        - rubble.se:5000/hemhub/api:latest
       labels:
         org.opencontainers.image.source: ${DRONE_GIT_HTTP_URL}
         org.opencontainers.image.revision: ${DRONE_COMMIT_SHA}
         org.opencontainers.image.created: ${DRONE_BUILD_FINISHED}
         org.opencontainers.image.version: ${DRONE_TAG:-${DRONE_COMMIT_SHA:0:7}}
+    when:
+      branch:
+        include: [ main, develop ]
+      event:
+        include: [ push, pull_request, tag ]
 
   - name: publish-tag
     image: plugins/docker
@@ -46,11 +47,16 @@ steps:
       tags:
         - ${DRONE_TAG}
       buildkit: true
+      cache_from:
+        - rubble.se:5000/hemhub/api:latest
       labels:
         org.opencontainers.image.source: ${DRONE_GIT_HTTP_URL}
         org.opencontainers.image.revision: ${DRONE_COMMIT_SHA}
         org.opencontainers.image.created: ${DRONE_BUILD_FINISHED}
         org.opencontainers.image.version: ${DRONE_TAG}
+    when:
+      event:
+        include: [ tag ]
 
 trigger:
   event: