refactor: Move GithubLink from ThemeToggle to AppHeader

[O2sa]

The GithubLink UI element is currently rendered inside components/theme-toggle.tsx but it belongs semantically in the application header. Move the GithubLink usage to components/app-header.tsx so header-related links are colocated and theme controls remain focused on theme toggling.

Tasks

• Remove the GithubLink import and usage from components/theme-toggle.tsx.
• Add import { GithubLink } from "./github-link"; to components/app-header.tsx (or the appropriate header file).
• Render the compact GithubLink inside the header (for example, next to the theme toggle or other header actions).
• Ensure styles and spacing match existing header controls and that accessibility attributes (aria-label) remain correct.
• Run the UI and smoke tests to verify there are no regressions.

Notes

• The GithubLink component is defined in components/github-link.tsx. The change is purely a structural/movement refactor; no API changes are required.
• This makes components/theme-toggle.tsx responsible only for theme switching behavior and keeps header links consistent in one place.

Testing

• Theme toggle still functions as expected with GithubLink removed.
• Header displays the GithubLink compact variant and link opens repository in a new tab.
• No visual regressions on desktop and mobile widths.

Tip

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[namahu]

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[github-actions]

🎉 Issue assigned to @namahu! Happy coding!