Sidebar: 'Open in GitHub' link in the Source Control panel

[thetechjon]

Context

The Source Control panel in the sidebar shows the configured sync repo + recent commits. There is no quick path from there to the GitHub UI for the vault, which users need for branch management, repo settings, releases, issues, etc.

A small external-link button next to the repo name would close the gap.

Where to look

• src/components/sidebar/SourceControl*.tsx — the sidebar Source Control panel. Files use the vscg naming convention (VS Code-style source control).
• src/stores/githubStore.ts — has the syncRepo shape { owner, name, branch, isPrivate }.
• @heroicons/react/24/outline — ArrowTopRightOnSquareIcon is the conventional "external link" icon.

Acceptance criteria

• When a syncRepo is configured, a small icon button appears next to the repo name in the Source Control panel header.
• Clicking the button opens https://github.com/<owner>/<name> (and .../tree/<branch> if branch is non-default) in a new tab with rel="noopener noreferrer".
• When no syncRepo is configured, the button is hidden.
• Hover tooltip says "Open in GitHub" (the existing data-noteser-tip system handles tooltips — see TooltipLayer.tsx).
• No regression in the existing panel layout on mobile (the icon should not push the repo name off screen).

Complexity

Tiny.

For first-time contributors

Read CONTRIBUTING.md. npm install, npm run dev. PR against dev.