fix: build JAR locally, use minimal JRE image

.gitea/workflows/build.yml

@@ -15,7 +15,7 @@ jobs:
     steps:
       - name: Install build tools
         run: |
-          apk add --no-cache curl git docker-cli 2>/dev/null || true
+          apk add --no-cache curl git docker-cli maven openjdk17 2>/dev/null || true
 
       - name: Clone + prepare
         run: |
@@ -25,6 +25,11 @@ jobs:
           cd "$WORK"
           git clone https://joe:${GITEA_TOKEN}@git.cjjhc.top/joe/${{ env.APP_NAME }}.git .
 
+      - name: Build JAR
+        run: |
+          cd /root/.cache/${{ env.APP_NAME }}
+          mvn clean package -DskipTests
+
       - name: Login to Harbor
         run: docker login ${{ env.REGISTRY }} -u admin -p "$HARBOR_PASSWORD"
         env: