fix(ci): remove stale GemReward gitlink

[zedarvates]

Summary

Repairs the repository-level checkout defect tracked in #48 without restoring or disclosing any submodule URL.

• removes the stale GemReward-Service-Repo gitlink;
• keeps the already-versioned public GemReward-Service-Staging/ tree unchanged;
• adds a minimal actions/checkout@v4 proof workflow with contents: read only.

Canonical-state evidence

• the gitlink was introduced in commit cdb9231 on 2026-03-08 without a matching .gitmodules entry;
• repository history contains no .gitmodules entry for this path;
• no tracked source or workflow references GemReward-Service-Repo;
• the public repository already tracks the GemReward implementation under GemReward-Service-Staging/;
• later commit 41d4225 only advanced the opaque gitlink commit and did not establish valid submodule metadata.

This makes deletion—not URL reconstruction—the smallest non-secret-bearing repair.

Validation

The PR's Repository Checkout CI job intentionally contains only actions/checkout@v4. A green run proves the repository can be checked out through the normal action without the semantic-prevalidator tarball workaround.

No private repository URL is added or exposed. No project code is changed.

Closes #48.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud