Initialize ci-core repository structure with composite action skeletons

[Copilot]

Establishes the foundational directory structure and placeholder files for centralized CI/CD components shared across OpenCB/Xetabase projects.

Structure Created

• .github/actions/setup-java-maven/action.yml - Composite action skeleton for Java/Maven environment setup with TODO comments for version inputs, dependency caching, and Maven configuration
• .github/actions/test-summary/action.yml - Composite action skeleton for test result collection and summary publication with TODO comments for result parsing and GitHub Actions UI integration
• .github/workflows/build.yml - Placeholder workflow file for validating composite actions

All actions include minimal viable YAML structure with name, description, and runs: using: 'composite' to establish valid GitHub Actions syntax. Placeholder steps prevent immediate failures when referenced before implementation.

Original prompt

Create the initial structure for a repository.

• Add a README explaining that this repo centralizes opinionated CI logic for all OpenCB/Xetabase projects.
• Create folders:
  .github/actions/setup-java-maven/action.yml
  .github/actions/test-summary/action.yml
• Both are composite actions with minimal skeletons and TODO comments, no real logic yet.
• Create a .github/workflows/ folder with an empty file build.yml

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[juanfeSanahuja]

@copilot I want to migrate two composite GitHub Actions from the repository opencb/java-common-libs into this new repository (ci-core).

Please do the following:

1. Fetch the code from branch TASK-8067 of opencb/java-common-libs for the two composite actions:

   • .github/actions/setup-java-maven/action.yml
   • .github/actions/test-summary/action.yml

2. Copy their full content into the corresponding files that already exist in this repository:

   • .github/actions/setup-java-maven/action.yml
   • .github/actions/test-summary/action.yml
     preserving formatting, comments and logic.

3. After that, modify branch TASK-8067 of opencb/java-common-libs:
   Replace all references to:
   .github/actions/setup-java-maven/
   .github/actions/test-summary/
   so they point to the equivalent locations in this repository:
   opencb/ci-core/.github/actions/setup-java-maven/
   opencb/ci-core/.github/actions/test-summary/

4. Ensure the “uses:” syntax follows the GitHub Actions reusable workflow/action format:
   uses: opencb/ci-core/.github/actions/setup-java-maven@main

Make sure all references are correctly rewritten and that the migration keeps the logic intact.