Fork workflow dispatch cannot download artifacts from the fork

[100yenadmin]

Summary

When the reusable Node/Java/Python workflows are dispatched in a fork with a
precompiled run ID from that fork, scripts/download-liblbug.sh still defaults
artifact lookup to LadybugDB/ladybug. The run ID is repository-scoped, so the
download returns HTTP 404 and the matrix fails before build or test.

Reproduction

1. Dispatch .github/workflows/precompiled-bin-workflow.yml in a fork.
2. Dispatch .github/workflows/nodejs-workflow.yml in the same fork with that
   successful run ID.
3. Observe gh run download "$RUN_ID" --repo LadybugDB/ladybug.

Observed failure:

HTTP 404: Not Found (.../repos/LadybugDB/ladybug/actions/runs/<fork-run-id>/artifacts)
Artifact liblbug-static-osx-arm64 does not contain liblbug-static-osx-arm64.tar.gz

The first error is the root cause; the missing-archive message is secondary.

Expected behavior

When LBUG_PRECOMPILED_RUN_ID is set in GitHub Actions, artifact lookup should
default to the current github.repository, while preserving
LBUG_GITHUB_REPOSITORY as an explicit override and preserving the canonical
upstream repository for release downloads.

Evidence

A one-line workflow-only override:

LBUG_GITHUB_REPOSITORY: ${{ github.repository }}

allows the existing script to download the exact fork artifact successfully.
This was validated locally before rerunning the fork matrix.

No publication or deployment is involved.

[100yenadmin]

Draft PR #684 implements the repository-scoped routing fix:
#684

Current head dfe57d7d is ready for review with 6/6 checks green. The
subprocess regression test covers:

• fork run IDs default to GITHUB_REPOSITORY;
• LBUG_GITHUB_REPOSITORY remains the explicit override;
• release downloads still default to LadybugDB/ladybug.

A real artifact download from fork run 29227829393 also passed without an
explicit repository override. No package or deployment action occurred.