update README for new systems, add GitHub Actions CI and remove GitLab CI support

[Yasu31]

No description provided.

[Copilot]

Pull request overview

This PR updates project onboarding and CI to reflect a move from GitLab CI to GitHub Actions, and modernizes the README’s platform/setup guidance.

Changes:

• Add a GitHub Actions workflow to build the project on Ubuntu and fetch submodules.
• Remove legacy GitLab CI configuration and the Dockerfile previously used for CI hints.
• Update README platform/support notes and dependency install instructions to reference the new CI workflow.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

File	Description
README.md	Updates supported platforms and setup guidance; points users to the new GitHub Actions workflow for dependency hints.
Dockerfile	Removed (previously provided Ubuntu build dependency hints).
.gitlab-ci.yml	Removed GitLab CI pipeline configuration.
.github/workflows/ci.yml	Adds GitHub Actions CI build on Ubuntu, including dependency installation and compilation.

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[Copilot]

Using ubuntu-latest can change the underlying OS version over time and make builds non-reproducible. Consider pinning to a specific runner image (e.g., ubuntu-22.04 or ubuntu-24.04) and updating intentionally when needed.

Suggested change

	runs-on: ubuntu-latest
	runs-on: ubuntu-22.04

[Copilot]

For stronger supply-chain security, consider pinning GitHub Actions to a commit SHA instead of a movable tag like actions/checkout@v4 (tags can be retargeted).

Suggested change

	uses: actions/checkout@v4
	uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4