Harden /capabilities: authorization + same-repo + exit handling - #63

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v2, actions/setup-java@v3, gradle/gradle-build-action@v2. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

Failed to restore v8-gradle|Linux|test examples-jvm[37a6259cc0c1dae299a7866489dff0bd]-ce1daf80cc08fadf5b2f346ef5cb8ddd79c7c8e0: Error: Cache service responded with 400