ci: unify on github-workflow-standard (build.yml + release.yml)

- maven.yml → build.yml: build-only, push (branches-ignore main, kein
  pull_request → keine Doppel-Läufe), concurrency, least-priv permissions;
  JDK-Matrix [11,17,21] behalten; mvn verify statt compile test.
- Action-Versionen auf latest major (checkout@v4, setup-java@v4).
- Toter ACCESS_TOKEN-Env-Var entfernt (in keiner pom.xml referenziert).
- release.yml: explizite permissions: contents: write (JitPack/README).
- Runner unverändert ubuntu-latest (kein self-hosted).

Standard: personal vault/concepts/github-workflow-standard.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: glaudeee

.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/maven.yml

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