GitHub Fork Compare Fix troch Nico

On a fork, GitHub points every compare and pull request link at the upstream repository — the Contribute menu, the "Compare & pull request" banner, and the "N commits ahead" link in the branch info bar. If you use your fork as a repository in its own right, that is the wrong target every single time, and opening a pull request against upstream by accident is far too easy.

This extension fixes that for the repositories you choose:

• Compare and pull request links point at your own repository, comparing your branch against your fork's own default branch.
• The branch info bar is restated against your default branch, so it reads exactly like a repository that is not a fork — with the real commit counts, not the ones relative to upstream.
• Links that mean the opposite (the "N commits behind" link) are left alone.
• Optionally redirects when an upstream compare page is already open.
• Enable a repository with one click from the toolbar, or list them as owner/repo or owner/* in the options page.

Repositories you have not enabled are untouched, so forks you genuinely contribute upstream from keep working exactly as before.

Privacy: no accounts, no tokens, no third-party requests, no telemetry. It reads github.com pages using your existing session and stores your list of repositories in extension storage. That is all.

Source code (GPL-3.0): https://github.com/D3SOX/gh-fork-compare-fix