ci: unify on github-workflow-standard

.github/CODEOWNERS

@@ -0,0 +1,3 @@
+# Code owner: auto-request review from codejanovic on every PR.
+# Enforce via branch protection "Require review from Code Owners".
+* @codejanovic

.github/workflows/auto-assign.yml

@@ -0,0 +1,24 @@
+# Sets codejanovic as ASSIGNEE on every PR (reviewer handled by .github/CODEOWNERS).
+name: Auto-assign
+
+on:
+  pull_request:
+    types: [opened, reopened]
+
+permissions:
+  pull-requests: write
+
+jobs:
+  assign:
+    if: github.event.pull_request.head.repo.full_name == github.repository
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/github-script@v7
+        with:
+          script: |
+            await github.rest.issues.addAssignees({
+              owner: context.repo.owner,
+              repo: context.repo.repo,
+              issue_number: context.issue.number,
+              assignees: ['codejanovic'],
+            });

.github/workflows/build.yml

@@ -0,0 +1,30 @@
+name: Build
+
+on:
+  push:
+    branches-ignore: [main]   # main = release branch → release.yml; PRs inherit via head SHA
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+
+jobs:
+  build:
+    name: Build for JDK ${{ matrix.java }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [11, 17, 21]
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up JDK ${{ matrix.java }}
+        uses: actions/setup-java@v4
+        with:
+          java-version: ${{ matrix.java }}
+          distribution: temurin
+          cache: maven
+      - name: Build & test
+        run: mvn -B -ntp verify

.github/workflows/release.yml

@@ -4,6 +4,9 @@ on:
   release:
     types: [published]
 
+permissions:
+  contents: write   # README version bump push
+
 jobs:
   trigger-jitpack:
     name: Trigger JitPack Build