ci: test installer across Linux distributions

[Mresyzz]

What this adds

Add a focused GitHub Actions check for install.sh whenever the installer or its tool-install helper changes. The workflow runs the real installer script in Debian, Ubuntu, and Alpine through OpsScript Gate v0.8.0, with the small explicit prerequisite set (bash, curl, ca-certificates, tar) and bridge networking required by the installer.

The report is uploaded even when a distro fails, so a maintainer can see which environment broke and why. Existing CI remains unchanged.

Why

The current CI builds and tests APX on hosted runners, but does not exercise the public Linux installer across distro-specific package and interpreter assumptions. This check catches those failures before a release reaches users.

Validation

• workflow is path-scoped to the installer and its helper
• checkout credentials are not persisted
• OpsScript Gate runs the target script without mounting the rest of the repository

[Mresyzz]

I validated this workflow in my fork against the real install.sh (run: https://github.com/Mresyzz/apx/actions/runs/36981847941). OpsScript Gate reached the download, checksum verification, and extraction stages on Debian 12, Ubuntu 22.04, Ubuntu 24.04, and Alpine 3.20. All four runs reproduced the same installer failure:

tar: ... Cannot change ownership to uid 1001, gid 1001: Operation not permitted

I opened a minimal follow-up fix for the installer: #52 (tar --no-same-owner). The temporary validation workflow has been removed from the fork after the run.

[Mresyzz]

After applying the follow-up fix on the fork branch, the same real matrix passed across Debian 12, Ubuntu 22.04, Ubuntu 24.04, and Alpine 3.20: https://github.com/Mresyzz/apx/actions/runs/36982358849

The temporary fork workflow was removed after validation. This gives the compatibility check a reproduced failure and a verified fix path.