feat: test only changed shell scripts in pull requests

[Mresyzz]

What changed

OpsScript Gate now supports PR-aware compatibility checks with --changed-since and the matching Action input. A pull request can test only changed shell scripts, skip container work when no shell script changed, and retain the existing discovery safety limits and filters.

This release also adds a self-hosted model installer guide using gpt-oss as a concrete use case. The guide clearly scopes the check to shell and distribution compatibility rather than GPU, model, or inference validation. The quickstart and generated workflow references are updated for v0.6.0.

Why this improves adoption

The default CI path no longer needs to run every discovered script for every documentation or application change. That makes the Action cheaper to adopt in real repositories and gives installer-heavy model projects a concrete entry point without claiming unsupported coverage.

Validation

• python -m pytest -q — 103 passed, 4 skipped
• python -m build — wheel and sdist built successfully for 0.6.0
• git diff --check
• Manual --changed-since origin/main --dry-run — empty selection returns success without Docker

Merging this PR will trigger the repository release workflow for v0.6.0 because the project version is updated to 0.6.0.