Set maven-compiler release to 8; add CONTRIBUTING and Java8 CI workflow

Author: juancadavid

.github/workflows/maven-java8.yml

@@ -0,0 +1,23 @@
+name: Java CI (Maven, Java 8)
+
+on:
+  push:
+    branches: [ main, master, toscaCodeGen ]
+  pull_request:
+    branches: [ main, master, toscaCodeGen ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: ['8']
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up JDK
+        uses: actions/setup-java@v4
+        with:
+          distribution: 'temurin'
+          java-version: ${{ matrix.java }}
+      - name: Build with Maven
+        run: mvn -B -DskipTests package

CONTRIBUTING.md

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+CONTRIBUTING
+
+Development setup
+-----------------
+This repository builds a Modelio 5.4.1 module (ToscaDesigner) and requires Java 8 for runtime compatibility with Modelio.
+
+Requirements
+- Java 8 JDK (for running Modelio and for building modules targeting Modelio)
+- Maven 3.6+
+
+Build instructions
+------------------
+From the project root:
+
+```powershell
+mvn -B -DskipTests package
+```
+
+This produces `target/toscadesigner-<version>.jar` and `target/ToscaDesigner_<version>.jmdac`.
+
+Notes
+-----
+- The project compiles with `maven-compiler-plugin` configured to `<release>8` to ensure bytecode compatibility with Modelio 5.4.1.
+- The `MDAKit` dependency is provided by the Modelio runtime; it is declared with `scope=provided` in `pom.xml`.
+- If you need to run checks that require the Modelio API, install Modelio and run integration steps inside its environment.
+
+Contributing
+------------
+- Fork the repo and create a feature branch.
+- Run the build locally and open a pull request.
+- For major changes, open an issue first to discuss the design.
+
+CI
+--
+A GitHub Actions workflow (maven-java8.yml) is included to build with Java 8 on push and pull requests.